The most probable and most likely answer to this problem would be C. revealed much about their behavior.
Out of the four options presented in this problem, C. would only need a complete subject to make it a correct sentence. Options A. by closely watching and gathering data and B. to terrifying effect would probably need other more words and/or phrases to make them more complete. D. insect studies, on the other hand, can also be considered as a correct option IF insect become the subject.
Brainstorming- collect textual evidence
First draft- expand on and write out ideas in full
Peer review- get suggestions for improvement
Answer: The differences between country and city life.
Explanation:
In this sentence it is an adverb :)
