Identify the sentence that contains a subject-verb agreement error.

The sentence "The group of students are studying" contains a subject-verb agreement error because the subject "group" is a collective noun that is treated as singular in American English. Therefore, the correct verb form should be "is" to agree with the singular subject. The focus here is on the collective entity (the group) rather than the individual members (the students). Collective nouns generally take a singular verb when the group acts as a single unit, which establishes the importance of making sure that the verb form matches the singular nature of the noun in this context. In contrast, the other sentences correctly match singular or plural subjects with their respective verb forms.