The subjects are not always in question before the verbs. Be sure to identify the subject accurately before opting for the right verb form. Subjects and verbs must correspond in number (singular or plural). So, if a subject is singular, its verb must also be singular; If a subject is plural, its verb must also be plural. Either. Or not. . nor, or, and again take two names before and after them. Names placed after these conjunctions are considered subjects of the sentence. Nouns that are placed before words or and again, have no influence on verbs. Example: the quality of the apples was not good. In it, the theme is the “quality of apples” and the verb is “were”.
As the theme “the quality of apples” is singular, instead of “were”, the singular “was” should have been used. So the right sentence is this: the quality of the apples was not good.