The correct answer is D) a double lift. A double lift is the appropriate method for hoisting a crew member requiring assistance during a medevac operation. This involves using two separate hoisting devices, such as rescue litters or baskets, to safely transport the individual to the aircraft. The double lift provides additional support and stability compared to using a single rescue device, which is crucial when dealing with an injured or incapacitated person. The other options, such as a rescue net or a single rescue litter, would not be as suitable for this scenario as they do not offer the same level of support and control during the hoisting process.