Question

which of the following is a valid criticism of investigations a and b? their participants are too young for the experiment. random group assignment means unequal groups. unequal groups; results are invalid. they endanger subject health; may be unethical.

Explanation:

In scientific investigations, if the groups are unequal, it can skew the results and make them invalid. Also, endangering subject - health is a major ethical concern in research. The criticism about participants being too young would need more context about the nature of the experiment, and random group assignment doesn't necessarily mean unequal groups.

Answer:

Unequal groups; results are invalid.
They endanger subject health; may be unethical.