Final answer:
The only verb listed in the sentence about cell phones is 'are,' making option b.) are the correct choice. It's important to apply the correct subject-verb agreement when choosing verb forms in other sentences.
Step-by-step explanation:
The verbs listed in the sentence "In the United States, cell phones are a very popular item" are contained in option b.) are. The word 'popular' is an adjective describing the noun 'cell phones,' and 'Today, are, popular' includes unnecessary information that is not part of the original sentence. Therefore, the correct answer indicating all the verbs in the sentence is b.) are.
When reviewing other questions regarding verb usage, it's essential to consider the subject-verb agreement in each sentence to choose the correct form of the verb.