A college wants to study if there is a relationship between the health of students enrolled at the university and the number of credit hours they are enrolled in. They pull the student numbers of all students who used the gym in the last month and randomly selected200. They then asked them how many hours he/she exercised in the last week and how many credit hours he/she is enrolled in and based on the data announced that the fewer credit hours a student is enrolled in at the university, the more hours per week the student exercises. Is this a valid conclusion?

a) No, the sample is biased because the sample was too small.

b) No, the sample is biased because only students at one university were questioned.

c) No, the sampling frame in this study introduced bias because it is not representative of the population.

d) Yes, the study was conducted in a fundamentally random way.