Mr. smith thinks his new smoothie recipe is the best ever. He believes it gives people more energy and also helps them lose weight. In order to prove this, he sets up an experiment. He randomly assigns 1/3 of his subjects to drink 1 smoothie per day for 10 weeks. The next 1/3 are andomly assigned to drink one smoothie per week for 10 weeks. The rest are assigned to 1 large cup of water per day for 10 weeks. What is the control group?

a) 1 smoothie per day
b) 1 smoothie per week
c) 1 large cup of water per day
d) no control group