Answer: D) Nozzle gimbals
Explanation: Igniters are present for the ignition power in the segmented solid rocket, liners are the basic requirement in the engine of the rocket,O-rings are also a general part of the segmented solid rocket .So, these are the general purpose parts of the segmented solid rocket but nozzle gimbals are the special units of the rocket as they provide improved thrust in various direction in accordance with the rocket.So, option (d) is the correct option.