Answer:
B. On average, how many plants do the students in your class have at home?
Explanation:
A statistical question must have the characteristic of variability, that is, it must be a question that can be answered by a collective, where each person has a slaightly or big different answer, because all of them are different, that's the variability ingredient.
Among the options, you can notice that only B has this characteristic, it's the only statistical question. In other words, question A and C are questions about one person, they don't have variability.