The stratosphere is a part of the atmosphere—specifically, a layer within it.
Similarly, a jet is a type or part of a larger category—aircraft.
Both pairs reflect a subset or component-category relationship.
Other options:
(a) Nimbus and Cloud are reverse; Nimbus is a type of cloud, not the other way.
(b) Instrument and Calibration show usage, not category.
(d) Climate and Rain are loosely related, but not part-whole in a structured way.
Thus, (c) is the most logically parallel.