Refer to figure.

This question is unnecessarily long and wordy, but does give some hints which help to remove incorrect options quickly.

Static stability pertains to how a system reacts immediately when disturbed. In a statically stable system, it initially moves back toward its equilibrium state. An aircraft's type of static stability is defined by its initial reaction after some external force is removed. We use the term "static" because we're only concerned with the initial tendency to return to equilibrium, without considering subsequent motion.

Manoeuvrability/controllability, on the other hand, are similar terms (not quite the same), and are the aircraft's ability to change its position or attitude in response to pilot inputs, allowing it to perform various manoeuvres.

The more stable an aircraft is, the less controllable, and vice versa.

The only option that makes any sense is "to make it easier to return to steady flight after being disturbed by an external force" as the other options either describe low stability or fuel efficiency, which is not related.