Hey there!
A scientific question here would be our hypothesis, which would be written like this:
How does the (independent variable) affect the (dependent variable)?
This means your answer is A.
It is written in the form of a hypothesis and a scientific questions. The others don't address something that you can do an experiment on, and are just opinions/questions that can be answered with a fact. With A, you could carry out the experiment shown in the picture as the answer choice and picture correspond.
Hope this helps!