Answer:
The sentence which uses the given definition of the word comparative is the following one:
The teacher instructed her students to write a comparative essay.
Step-by-step explanation:
A comparative essay is a style of writing which aims at comparing at least two items that belong to the same category, so the comparison makes sense and is fair. Eg: a comparative essay on Edgar Allan Poe's and Arthur Conan Doyle's detective stories. Therefore, the adjective "comparative", meaning "measured by comparison with others", appears in the aforementioned sentence.