VINCI is a very large, investment-grade infrastructure/concessions and construction group with strong access to debt markets and meaningful recurring cash generation. In 2022 it generated €9.4bn of operating cash flow, €4.4bn of profit, and had substantial equity of €29.4bn against total assets of €112.0bn.

Its balance sheet already carries significant conventional debt: non-current bonds of about €20.4bn, other non-current borrowings of €3.2bn, short-term borrowings of €6.4bn, and lease liabilities of about €2.1bn. However, liquidity is also strong, with cash and cash equivalents of €12.6bn. Equity increased materially in 2022, and profitability recovered strongly, so there is no urgent need to use hybrid instruments as a major balance-sheet repair tool.

Hybrid bonds could still be useful for VINCI because:
- it has long-duration infrastructure/concession assets that can support long-dated capital;
- hybrids may receive partial equity credit from rating agencies;
- they can help preserve credit metrics while funding acquisitions or concessions growth;
- VINCI is large enough and creditworthy enough to access the hybrid bond market efficiently.

But a high reliance on hybrid bonds is not warranted. The 2022 rate environment rose sharply: 5Y, 7Y and 10Y swap rates increased to around 1.7%–1.9%, while corporate credit yields/spreads also rose. Hybrid/subordinated debt would be more expensive than senior debt, and VINCI’s strong ordinary debt-market access reduces the need for heavy hybrid issuance. Too much hybrid debt would add coupon cost, refinancing complexity, and potential investor/rating-agency limits.

Therefore, hybrids should play a moderate, supplemental role rather than dominate the capital structure. Among the choices, 25% is the most appropriate: enough to benefit from equity credit and funding flexibility, but not so much that it materially increases structural subordination or financing cost.

<answer>25%</answer>