Final answer:
The sentence 'Every one of the shirts has a green collar.' is correct because 'every one' is a singular subject and requires a singular verb, which is 'has' in this context.
Step-by-step explanation:
The correct sentence with the proper subject/verb agreement is: Every one of the shirts has a green collar. In this sentence, 'every one' is the subject which is singular, and it should be followed by a singular verb, which is 'has' in this case. The phrase 'every one' refers to each individual item in a group, each being considered separately, thus it takes a singular verb.
Indefinite pronouns such as everyone, each, every one, nobody, anybody, someone, and nobody typically require a singular verb. This is an important rule to remember when working on subject-verb agreement.
When checking for subject-verb agreement, ensure that if the subject is singular, the verb must also be singular, and if the subject is plural, the verb must be plural. The complexity of subject-verb agreement lies in the grammatical number of the subject. Singular subjects take singular verbs, while plural subjects take plural verbs.