The Following Are Reasons for Studying Randomized Controlled Experiment in an Econometrics

The following are reasons for studying randomized controlled experiment in an econometrics course, with the exception of

A) at a conceptual level, the notion of an ideal randomized controlled experiment provides a benchmark against which to judge estimates of causal effects in
Practice.
B) when experiments are actually conducted, their results can be very influential, so it is important to understand the limitations and threats to validity of actual
Experiments as well as their strength.
C) randomized controlled experiments in economics are common.
D) external circumstances sometimes produce what appears to be randomization.