What is a major problem with nonequilvalent groups _______
(a) the groups may differ on the dependent measure(s) at the start of the study
(b) there may be confounding variables not controlled by random assignment
(c) the groups may differ on independent measure at the start of the study
(d) both a & b
This question is tackled.
I think you're right in saying that a) is right - nonequivalent groups could definitely differ on the DV (ie. on what is being measured).
As for b), if you have random assignment, you should have confounding variables controlled for. That is, ...
Nonequivalent groups are briefly explored in a multiple choice question.