a virus suspended in the air an accident on a playground a genetic mutation in somatic cells an occurrence of acid rain
I gave my students this multiple choice question: What condition is most likely to spread an illness between people?

Only one answer is correct among these 4 choices:
- a virus suspended in the air
- an accident on a playground
- a genetic mutation in somatic cells
- an occurrence of acid rain

Could you tell me which one is correct?

a virus suspended in the air