Which of the following items is unique to C-17s?

The uniqueness of the item to C-17s is due to the specific design and functionality that the C-17 offers for airborne operations. The C-17 is engineered to facilitate a diverse range of cargo operations, and one aspect of this functionality is its capability to employ two static line retrieval systems effectively. This system is designed to enhance the efficiency of jump operations by allowing for simultaneous retrieval of two static lines, which is particularly beneficial during mass tactical drops.

In comparison, other choices like the static line delivery system and the cargo lift system are not exclusive to the C-17, as they can be found in various aircraft designed for similar operational roles. The emergency release system is also applicable to several aircraft types, aimed at ensuring safety and quick release of cargo in emergencies. The distinct feature of having two static line retrieval systems is a specialized adaptation for the C-17, emphasizing its versatility and effectiveness in transport and aerial delivery missions.