B is correct.

The option on futures using the BSM model is expressed as follows:

c = F₀e⁻ʳᵀN(d₁) − Ke⁻ʳᵀN(d₂)

where:

• F₀ = current futures price = EUR 63
• K = strike price of the option on futures = EUR 68
• T = time to expiration of option = 0.5 (6 months)
• r = risk-free interest rate = 3%
• N(d₁) = 0.4678
• N(d₂) = 0.3449

Calculation:

• F₀e⁻ʳᵀ = 63 × e^(-0.03 × 0.5) = 63 × e^(-0.015) = 63 × 0.98511 = EUR 62.062
• Ke⁻ʳᵀ = 68 × e^(-0.03 × 0.5) = 68 × 0.98511 = EUR 66.988
• c = 62.062 × 0.4678 − 66.988 × 0.3449
• c = 29.029 − 23.105
• c ≈ EUR 5.93

Note: The time to maturity of the underlying futures contract (18 months) is not used in the BSM formula for pricing options on futures. Only the time to expiration of the option (T = 0.5 years) is used.