A company is testing a new protein shake which they claim works better than their existing brand in improving an athlete's performance. The company selected 60 athletes from a training camp database, and divided them into three groups. The ages for the groups were 16 to 20 years, 21 to 25 years, and 26 to 30 years. In each group, half of the subjects were asked to use the new protein shake for a month, and the other half were asked to use the company's existing brand for a month. The subjects were not informed about which protein shake they would be using.

Which statements about this study are true?

The study uses blocking on the basis of gender.
The study uses a repeated measure design to reduce variability from unknown factors.
The study uses random sampling.
The study uses blocking to reduce variability from known factors.
The study does not use a control grou