Four Students Plan to Conduct an Experiment with Four Conditions

Four students plan to conduct an experiment with four conditions (A,B,C,and D) during one semester.Each student will serve as an experimenter.The best way to control for the extraneous variable of having four experimenters test participants in the study is to

A) make sure each experimenter tests only one of the conditions.
B) have the first experimenter test a random order of conditions during the first two weeks of the semester, the second experimenter test a second random order during the next two weeks, and so on.
C) have each experimenter test randomized blocks of conditions.
D) have each experimenter test condition A during the first two weeks of the semester, condition B during the next two weeks, and so on.