What Is the Reason Online Experiments Have Been Slower to Gain

What is the reason online experiments have been slower to gain popularity when compared to online surveys?

A) Experimental design often requires that participants don't do more than responding to questions.
B) Experimental design often requires that participants do something more active than responding to questions.
C) It is much easier logistically to do experiments online as opposed to surveys.
D) Online experiments are cheaper but take less time.