A student states that exercise will affect the number of times a person can squeeze a clothespin in a certain amount of time. An experiment is carried out to test this hypothesis. One group of ten students sits quietly before squeezing a clothespin as many times as possible during a one-minute interval. A second group of ten students does 25 jumping jacks before squeezing a clothespin as many times as possible during a one-minute interval. What is one way this experiment could be improved in order to increase the validity of the results?

A) change the exercise type from jumping jacks to jogging in place

B) increase the number of students in each group

C) reduce the number of trials performed

D) allow the group of sitting students to talk first