The following sentence has been split into four segments. Identify the segment that contains a grammatical error.
They / was / reading / a notice.

Correct option is C

The segment containing a grammatical error is (c) "was." The correct segment should be "were" as the subject "They" is plural. Subject-verb agreement requires verbs to agree in number with their subjects. "They" is plural, thus necessitating the plural verb "were." Grammatical rule used: Subject-verb agreement with plural subjects. Example: They were excited about the upcoming trip.