Read each sentence to find out whether there is any grammatical or idiomatic…

Read each sentence to find out whether there is any grammatical or idiomatic error in it. The error, if any, will be in one part of the sentence. The number of that part is the answer. If there is 'No error', the answer is 'e'. (Ignore errors of punctuation, if any.)

It had (A)/ stopped raining (B)/ when I (C)/ had left the office. (D)