The correct answer to the question is A: Buy the forward contract and buy the zero-coupon bond. This strategy creates a synthetic long position in commodity X for a period of 6 months. The explanation for this is based on the concept of creating a synthetic commodity position through a combination of a long futures contract and a zero-coupon bond.

A synthetic commodity position for a period of T years can be constructed by entering into a long futures contract with T years to expiration and buying a zero-coupon bond expiring in T years with a face value of the present value of the futures price. The payoff function at time T is as follows:

• Payoff from long futures position = $S_T - F_{0,T}$, where $S_T$ is the spot price of the commodity at time T and $F_{0,T}$ is the current futures price.
• Payoff from zero coupon bond = $F_{0,T}$

Hence, the total payoff function equals $(S_T - F_{0,T}) + F_{0,T}$ or $S_T$. This creates a synthetic commodity position that replicates the payoff of owning the actual commodity.

Options B, C, and D are incorrect because they do not replicate the payoff of a long position in the commodity. Buying the forward contract and shorting the zero-coupon bond (option B) or shorting the forward contract and either buying or shorting the zero-coupon bond (options C and D) would not result in a synthetic long position in the commodity.