I need help UwU

I cant do this and its my last question help plz

I’m doing some practice exam questions for biology, and i’m not sure how to do these 3 parts to the question.

Cedric has a low fever and minor aches. yesterday, he went to the doctor for his booster shot and receive the flu shot. which best explains why he has this reaction?

In the practice of science, this type of reasoning is used to develop explanations.