The correct answer is A. Experimental
Step-by-step explanation:
In an experiment where two groups are being used to test a hypothesis or possible explanation to a phenomenon, the experimental group is the one in which the researcher intervenes or the one that receives special treatment. Moreover, the experimental group is the opposite of the control group that is the group with no treatment used as a standard in the experiment. This means, in BIll's experiment it is group A the experiment group because this is the group that receives training and therefore it is the group Bill is intervening.