The Major Advantage of Free-Operant Methods Over Discrete Trial Procedures

The major advantage of free-operant methods over discrete trial procedures is that

A) the animals learn more quickly.
B) free operant methods provide the opportunity to observe changes in the likelihood of behavior over time.
C) free operant methods can reveal an animal's preferences.
D) free-operant methods involve S-S learning, but discrete trial procedures involve S-R learning.