In this question, a sentence has been divided into four parts (A), (B), (C) and (D). Read the sentence to find out whether there is any grammatical error in it. The error if any, will be in one part of the sentence. Mark that part as your answer. If there is no error, the answer is ‘No error’. Ignore the error of punctuation if any. 

While scientists have proposed (A)/ many theories around the origin of the Moon,(B)/ deeper investigation into other planetary bodies (C)/ has complicated each hypothesis.(D)