Select the grammatically correct sentence.

The correct sentence is: "The participants of the competition are waiting for their turn curiously."

To determine the grammatically correct sentence, we need to analyze the subject-verb agreement and article usage:
1. Identify the subject: In the phrase "The participants of the competition", the main noun (head noun) is "participants", which is plural. The phrase "of the competition" is a prepositional phrase modifying the noun "participants" and does not affect the number of the verb.
2. Determine the correct verb: Since the subject "participants" is plural, it requires a plural verb. Therefore, we must use "are" instead of "is" or "has".
3. Check the article: "A" is an indefinite article used with singular countable nouns (e.g., "a participant"). Using "A" before the plural noun "participants" is grammatically incorrect.

Let's evaluate each option based on these rules:
- "The participants of the competition are waiting...": Correct. The plural subject "participants" correctly agrees with the plural verb "are".
- "The participants of the competition has been waiting...": Incorrect. "Has been" is singular and does not agree with the plural subject "participants".
- "A participants of the competition is waiting...": Incorrect. The singular article "A" is paired with a plural noun "participants", and the verb "is" is singular.
- "The participants of the competition is waiting...": Incorrect. The singular verb "is" does not agree with the plural subject "participants".