Which sentence contains an error in subject-verb agreement?

• A. One hundred pesos are hard to earn in one day.
• B. The Boy Scouts raised the flag.
• C. The staff is ready for the meeting.
• D. The books are on the shelf.

Answer: (A)

The main idea here is how to match a verb to a money amount when the amount is treated as a single quantity versus individual units. When you speak of a sum of money, it’s usually treated as one amount, so the verb should be singular. Saying “One hundred pesos is hard to earn in one day” treats the money as a single total, which fits the rule. The version with “are” makes it sound like you’re talking about one hundred separate pesos rather than the total sum, hence the mismatch.

The other sentences follow standard subject-verb rules. The Boy Scouts is a plural subject, so the past tense verb fits. The staff is a collective noun typically paired with a singular verb in American English, which is correct here. The books is plural, so the plural verb is appropriate.