exposure to hot weather decrease in physical exercise consumption of bad food infection by a virus
I gave my students this multiple choice question: Over a two-week period, several students complain of feeling sick. Their symptoms include a cough, fever, and a sore throat. What describes the most likely cause of these symptoms?

Only one answer is correct among these 4 choices:
- exposure to hot weather
- decrease in physical exercise
- consumption of bad food
- infection by a virus

Could you tell me which one is correct?

infection by a virus