Which sentence shows 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)

When an amount of money is used as the subject, treat the whole amount as a single unit, so the verb should be singular. In the sentence about one hundred pesos, the amount is a single total value, and it should take a singular verb: is. Using are creates a mismatch between the subject (the amount as a single unit) and the verb.

The other sentences show correct agreement: The Boy Scouts is a plural subject, so raised (a past tense verb) fits. The staff is a collective noun treated as a single entity here, so is is acceptable. The books are a plural subject, matching the plural verb are.

So the error lies in treating the money amount as plural with are instead of singular with is.