To determine the appropriate extent to which Iberdrola SA should rely on hybrid bonds in its capital structure, we must analyze the company's financial health, the cost of capital environment, and the strategic role of hybrid instruments.

**1. Analysis of Current Capital Structure and Financial Health:**
*   **Equity Base:** As of 2023-01-01, Total Equity is €58,114 million. Equity attributable to owners of the parent is €41,119 million.
*   **Debt Load:** Noncurrent Financial Liabilities are €44,216 million, and Current Financial Liabilities are €25,079 million, totaling roughly €69,295 million in financial debt.
*   **Hybrid Presence:** The balance sheet lists "Instrumentos De Capital Con Caracteristicas De Pasivo Financiero" (Financial Liabilities with Equity Characteristics) of €576 million (Noncurrent) and €87 million (Current). This represents a very small fraction of the total capitalization (less than 1% of equity).
*   **Leverage:** The Debt-to-Equity ratio (Financial Debt / Total Equity) is approximately 1.19x. This is a moderate leverage level for a utility company, which typically operates with higher leverage due to stable cash flows.
*   **Profitability:** The company generated a Net Profit of €4,339 million and an EBITDA of €13,228 million. Interest coverage is healthy, though finance costs rose to €3,042 million in 2022 from €2,268 million in 2021, reflecting the rising rate environment.

**2. Market Environment and Cost of Capital:**
*   **Rising Rates:** The swap curves show a dramatic increase in interest rates from 2021 to 2022. The 10Y swap rate went from an average of 0.053% in 2021 to 1.927% in 2022. The iShares Core Euro Corp Bond yield also rose from 0.733% to 1.085%.
*   **Cost of Hybrids:** Hybrid bonds (perpetual subordinated debt) typically carry a higher coupon than senior debt because they are riskier for investors (subordinated, deferrable interest). However, they are treated as equity for rating agency purposes, which helps maintain credit ratings without diluting existing shareholders.
*   **Spread Analysis:** The "Sub-Sen Delta" for iBoxx EUR Non-Financial IG indicates the spread between subordinated and senior debt. In 2022, the average spread was 2.295%. This means hybrid/subordinated debt is significantly more expensive than senior debt.

**3. Strategic Considerations for Hybrid Bonds:**
*   **Rating Optimization:** Utilities like Iberdrola rely heavily on credit ratings to keep borrowing costs low. Hybrid bonds count as equity for ratings (e.g., S&P, Moody's) but as debt for tax purposes (interest is tax-deductible, unlike dividends). This "tax shield" benefit makes them attractive if the company needs to strengthen its equity ratio without issuing new shares.
*   **Current Equity Position:** Iberdrola's equity base is strong (€58bn). The company does not appear to be in distress or dangerously over-leveraged. Therefore, there is no urgent *need* to issue large volumes of expensive hybrid capital to save the credit rating.
*   **Cost Efficiency:** Given the high cost of subordinated debt (spread of ~2.3% over senior), issuing too much hybrid debt increases the weighted average cost of capital (WACC) unnecessarily if the company can maintain its rating with standard debt and retained earnings.
*   **Standard Practice:** Most investment-grade utilities maintain a small portion of their capital structure in hybrids (typically 5-15% of total capitalization) to optimize the rating/equity mix. They rarely rely on them for 50% or more of their capital, as this would be prohibitively expensive compared to senior debt or retained earnings.

**4. Evaluating the Options:**
*   **0%:** While the current holding is low, completely avoiding hybrids removes a useful tool for rating management and flexibility. However, given the high cost in 2022, a minimal approach is viable. But "0%" implies a strategic decision to never use them, which is unlikely for a major utility.
*   **25%:** This would imply that 25% of the capital structure is hybrid. For Iberdrola, 25% of ~€127bn (Assets) or even ~€58bn (Equity + Debt) would be €15-30 billion. This is vastly higher than the current €0.6 billion. Such a high proportion would drastically increase interest expenses and WACC. It is too aggressive.
*   **50%, 75%, 100%:** These are excessively high and financially imprudent for a stable utility. They would imply a capital structure dominated by expensive, subordinated instruments, destroying shareholder value.

**Refining the "Extent" Interpretation:**
The question asks "To what extent *should* this company's capital structure rely on hybrid bonds?".
Looking at the data, Iberdrola currently has a very low reliance (<1%).
Is the question asking for the *optimal* target?
Standard corporate finance theory for BBB/A-rated utilities suggests a hybrid component of roughly 5-10% of total capitalization to optimize ratings.
However, the options are 0, 25, 50, 75, 100.
These are broad buckets.
Let's look at the "Noncontrolling Interests" (€16,995m) and "Equity Attributable to Owners" (€41,119m).
Total Equity = €58,114m.
Total Debt (Financial) = ~€69,300m.
Total Capital (Debt + Equity) = ~€127,400m.

If the company were to rely on hybrids for **25%** of its capital structure, that would be ~€31 billion. This is huge.
If the company relies on hybrids for **0%**, it relies entirely on Senior Debt and Equity.

Let's re-read the prompt's context. It provides market data showing rising rates. In a rising rate environment, the cost of *all* debt rises. Hybrids become even more expensive relative to senior debt if the spread widens or stays high.
Iberdrola's current hybrid usage is negligible.
Does the company *need* to increase it?
The leverage is manageable. The interest coverage is good.
Usually, "reliance" on hybrids is a strategic choice to boost equity ratios.
If we look at peer groups, hybrids often make up a small single-digit percentage of total capital.
Among the choices, **0%** is the closest to the current reality and arguably the most prudent *primary* source of funding, given that hybrids are a niche, expensive instrument. However, completely ruling them out (0%) is rigid.

Let's consider if the question implies a classification of the *current* state or a *recommendation*. "To what extent *should*..." implies a recommendation.
Given the high cost of subordinated debt (2.295% spread over senior IG), and the fact that Iberdrola has strong retained earnings (€20,310m) and cash flow, it should prioritize internal equity generation and senior debt. Hybrids are a marginal tool.
Compared to 25%, 50%, etc., 0% is the most defensible "base" answer if we interpret "rely on" as "depend on as a major pillar". It should not *rely* on them. It might *use* them sparingly.

However, often in these multiple-choice financial logic questions, if a company has *some* hybrids, and they are beneficial for ratings, the answer might not be 0%. But 25% is way too high.
Let's look at the "Instrumentos De Capital..." line item again. It is €576m + €87m = €663m.
Total Capitalization (Equity + Net Debt) is approx €127 Billion.
Current reliance is ~0.5%.
Rounding to the nearest option: 0%.

Furthermore, in a "Bear" market scenario (high rates), the cost of hybrids spikes. The provided data shows 2022 was a "Bear" year for bonds (yields up). The spread for Sub-Sen was 2.49% in Bear. This makes hybrids very expensive. A prudent CFO would minimize reliance on this expensive capital when senior debt and retained earnings are available.

Therefore, the company should not *rely* on them. It should use them minimally if at all. The best fit among the discrete options is 0%.

<answer>0%</answer>