Explanation
The blank should mean “returning” or “reappearing”, something that matches “hearken back” and “signs today.”
A. evanescent means fleeting, temporary: not the main idea; it’s about reappearing, not disappearing quickly.
B. resurgent means increasing again, reviving: fits.
C. recrudescent means breaking out again (especially of something undesirable): fits.
D. transitory means temporary: not the point.
E. controversial means debatable: possible but not directly supported by the context about “hearken back” and “signs today.”
F. inimical means harmful, hostile: not directly supported by the sentence’s main point of “coming back.”
The best pair is B and C, both mean reappearing/reviving.
Answer: B, C