Answer:
The answer is "one"
Explanation:
Great question, it is always good to ask away and get rid of any doubts that you may be having.
Based on the sentence that is in the question we can see that it is mentioning a singular person, therefore we can cross out the last two options since they mention imply various people. So we are left with the first two option.
If we plug in the first answer we can see that it is grammatically incorrect. This being the case we are left with only one answer and since it is grammatically correct then the final answer is "one".
I hope this answered your question. If you have any more questions feel free to ask away at Brainly.
