Final answer:
The correct sentence is 'One of the girls has given up her seat,' with 'has' and 'her' being the correct singular forms to match the singular subject 'One of the girls.'
Step-by-step explanation:
The subject of the sentence in question is 'One of the girls,' which is singular. Therefore, the correct verb to use is 'has,' not 'have.'
Similarly, the pronoun should match the subject in number, so 'her' is appropriate rather than 'their.' Lastly, 'seat' should be singular to match the singular subject and pronoun, so the correct sentence is 'One of the girls has given up her seat.'
In English grammar, it's crucial to ensure that the subject and verb agree in number. For example, 'The folks at my school' is a plural subject, so the correct verb form is 'voted,' not 'votes.'
Similarly, when dealing with indefinite pronouns like 'everyone,' the verb agreement should be in the singular form since 'everyone' refers to each person in a group individually, not the group as a collective.
Understanding subject-verb agreement helps one write clear and grammatically correct sentences. It's an essential skill for effective communication in both written and spoken English.