If the Experimental and Control Groups Both Improve Significantly, Then

Multiple Choice

If the experimental and control groups both improve significantly, then we should conclude that:

A) the intervention and control conditions both were causes of the improvement.
B) the results do not support the notion that the intervention is effective.
C) some alternative explanation like history or the passage of time plausibly could have caused the improvement in both groups.
D) Both b and c are correct.