For Which of These Empirical Questions Would a Control Group

Multiple Choice

For which of these empirical questions would a control group most clearly be needed?

A) If institutionalized elderly are given responsibility for meal planning, will it improve their psychological health?
B) Do laboratory-bred rats learn mazes faster than wild rats?
C) If participants are trying to solve problems, will they perform better in the morning or the evening?
D) Will an attractive female defendant be treated more leniently by a jury than an attractive male defendant?