59.
Your Answer is
Correct Answer is D
Explanation
As the leading adverbial clause, the subject of the main clause is hundreds of tiny fireflies, so the predicate verb of the main clause should appear in the underlined part, and item D is correct.
Item B/C: Both are attributive clauses, so that the main clause has no verbs, which is wrong.
Item A: It is a non-predicate verb, wrong.