Read the sentence to find out whether there is any error in it. The error, if…

Read the sentence to find out whether there is any 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 (5). Ignore errors of punctuation, if any.

No sooner had (1)/ he begun to speak (2)/ when the opposition members (3)/ started shouting slogans. (4)/ No error (5)