Students from Two Groups Were Sent One-At-A-Time into a Room

Students from two groups were sent one-at-a-time into a room to receive a set of instructions pertaining to four simple tasks they were supposed to perform. The first group was met by a kindly individual who carefully explained in a cheerful manner what was expected of them. The second group was met by the same man, but this time he was angry and aggressive and forcefully demanded compliance. The experimenter then left the room and each student was observed through a one-way mirror to see how long it took them to complete all four tasks. The independent variable in this experiment is __________

A) time required to complete the four tasks.
B) the demeanor or attitude presented by the experimenter.
C) the number of tasks the students were required to perform.
D) the isolation of the students.