The subject and verb of any clause must agree in both person and number. The parents were proud of the student.
Compound subjects connect with and usually require a plural verb.
Singular subjects joined by nor or or take a singular verb. Neither Jim nor Holly is ever going to finish graduate school. The indefinite pronouns each, either, neither, one, anyone, everybody, another, anybody, everybody, nobody, everything, somebody, and someone are singular. There are exceptions to every rule. Some nouns which are plural in form but singular in meaning take a singular verb.