Which of the following sentences has an incorrect subject-verb agreement?

The sentence "Many of the people attending the trial seems upset" presents an incorrect subject-verb agreement because the subject "many" is plural, while the verb "seems" is singular. When the subject of a sentence is plural, the verb should also be in the plural form to maintain agreement. The correct verb form that corresponds to the plural subject "many" would be "seem." This ensures that the subject and verb agree in number, which is a fundamental rule in English grammar.

In contrast, the other sentences each feature a singular subject paired with a singular verb or are structured in a way that maintains correct agreement. For instance, "The Society of Women Voters seems to be having a banquet" uses a singular verb "seems" with the singular entity "Society," and "A ten percent failure rate seems too high" aligns a singular subject with a singular verb. Similarly, in the sentence "Everyone in the family seems happy," "Everyone" is a singular pronoun, correctly paired with the singular verb "seems." Thus, understanding subject-verb agreement is essential for constructing grammatically correct sentences.