A. They may be more ethical than experiments.
B. they control for extraneous variables.
C. potentially large amounts of data can be collected.
D. both A and C

I think its E. None of the above... but then its your homework assignment and not ours. And we don't do anyone's homework assignments.

What do you think the answer is and why? We only help after you show us you have tried... and then help you arrive at the answer yourself, but you won't get your answers handed to you without you doing the work. You will learn nothing and will fail your class otherwise.