Which sentence has an error in subject-verb agreement? a) the pile of leaves that had been sitting at the end of the road for weeks began to decompose slowly. b) there are entirely too many ketchup bottles in the refrigerator, and some of them must be thrown away. c) unlike most runners, charles--even if parched--would never drink any water at any point during the run. d) the man, in the next apartment, as well as the people across the hall, have lived in the building since 1960.

The answer is:

D) The man, in the next apartment, as well as the people across the hall, have lived in the building since 1960.

Subject-verb agreement means that the subject and the verb must possess the same number. Thus, when the subject is singular, the verb must be singular; and when the subject is plural, the verb must be plural too.

In sentence D, there is no subject-verb agreement because the subject is singular (the man) and the auxiliary verb is plural (have). The correct sentence is:

The man, in the next apartment, as well as the people across the hall, has lived in the building since 1960.