Dr Bischer Is Conducting a Study to Determine If Men

Dr. Bischer is conducting a study to determine if men who wear a new type of soccer uniform made from a specially designed fabric will perform better in soccer matches. She recruits a professional soccer team to participate. She randomly assigns half of the men to wear the new-material uniforms made in the color blue and the other half to wear old-material uniforms made in the color red. Although the men know of the uniform test, they are not told which of the uniforms is made from the new material. They are asked to wear their assigned uniforms and score as many goals as possible in a practice scrimmage game against one another. Dr. Bischer is noting the number of goals scored. Ultimately, the men who are wearing the old uniforms score more goals and therefore win the game. Dr. Bischer speculates that the new uniforms are not more beneficial to performance than the old uniforms, but she will rerun her study a few more times.
-From a scientific viewpoint, why was it important for Dr. Bischer to randomly assign the men to wear new uniforms or old uniforms?

A) Some of the men will feel it was unfair that they did not get new uniforms and will not be motivated to be competitive-in this case, therefore, the uniform assigned was simply the luck of the draw.
B) She wanted to the men to feel they all had a chance of wearing their old uniforms, in which they would likely be more comfortable.
C) Some of the men who could not participate that day were then used as a control group, and she wanted to make sure she had an even number of new and old uniforms left over.
D) She wanted to ensure that the two groups were, on average, similar in ability and motivation, so that any differences in the end would be due to the experimental manipulation.