Nay, it is in fact C) She is lonely and sad, but determined to preserve.
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.
Actually there are some exceptions in some cases though: a/an
example: "not only is there 3 species, but there is a 4th specimen."
Answer:
B) Toe dancing was developed in the early nineteenth century, but it was not widely used until the 183s.
Explanation:
At first, I thought the answer was D because it showed a contrast, but then I realized there should probably be a comma after "however" so the answer is most likely B.
Hope this helps and is the right answer :)