55.
Your Answer is
Correct Answer is C
Explanation
According to the meaning of the sentence, the underlined part is to explain the reason of the previous half sentence. C is correct.
Item A: After the error and, it should be a complete sentence, here is an attributive clause.
Item B: which guides the attributive clause to be the subject or object in the clause, and there is no lack of subject or object behind this sentence.