In a Complex Design Experiment,researchers Found That Younger and Older

Multiple Choice

In a complex design experiment,researchers found that younger and older people performed equally well on a memory task when they were tested in the afternoon,but the older people performed better than the younger people when they were tested in the morning.The different effect of age at the two times of day represents

A) a main effect.
B) an interaction effect.
C) a correlational effect.
D) a simple comparison effect.