The sentence that has an error in subject-verb agreement 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 of a sentence and the verb must agree in number. That is to say, both of them need to be singular or plural. In sentence D, the subject of the sentence is "the man" and the verb is "have lived". As the sentence refers to one man, the verb should be "has lived" in order to agree in number with the subject.
