Please I need an answer to this question:

Thanks a lot.

Researchers want to test the effects of a new weight loss program. They believe that gender is a significant factor. The participants are divided by gender. Then, within each group, participants are randomly assigned to either the treatment or control group. Which of the following would be the most effective to test the effects of the new weight loss program? 0 A matched-pair design experiment 0 A completely randomized design experiment 0 A randomized block design experiment 0 A longitudinal observational study