Study 1: An economist conjectures that people will perform worse on a skill-based task when they are in the presence of an observer with a financial interest in the outcome. She conducted the following study, in which a total of 42 participants played a video game that required them to get Sonic the Hedgehog to the end of an obstacle course as quickly as possible. Subjects were randomly assigned to one of two groups. One group was told that the participant and observer would each win $10 if the participant beat a certain threshold time. The other group was told that only the participant would win the prize if the threshold were beaten, and that the observer had no stake in the outcome. Her analysis revealed that the two groups had no difference: they both met the threshold time at about the same average rate.

Study 2: A financial planner conjectures that consumers with poor credit histories will benefit from receiving free credit-counseling services. She spent several weeks recruiting study participants at car dealerships. She ultimately collected a sample of 155 consumers who were shopping for a new car, but had reported difficulty in securing a loan to make the purchase. All 155 of these consumers were offered free credit-counseling services, and 94 accepted the offer. Of the 94 consumers who received credit counseling, 84% managed to secure a car loan within 6 months. Of the 61 who did not receive counseling, only 49% managed to get a loan.

One of these studies has a notably superior experimental design. Which is it, and why?

(a) Study 1, because it has both a treatment group and a control group.

(b) Study 2, because it has a larger sample size.

(c) Study 1, because it randomized participants to treatment and control groups.

(d) Study 2, because it showed a difference between the two groups (whereas Study 1 showed no difference).

I want to say that it is either B or C, but I am unsure of which between the two. Thanks.