In one study on the effect that eating meat products has on weight level, an SRS of 500 subjects who admitted to eating meat at least once a day had their weights compared with those of an independent SRS of 500 people who claimed to be vegetarians. In a second study, an SRS of 500 subjects were served at least one meat meal per day for 6 months, while an independent SRS of 500 others were chosen to receive a strictly vegetarian diet for 6 months, with weights compared after 6 months.
(A)The first study is a controlled experiment, while the second is an observational study. (B)The first study is an observational study, while the second is a controlled experiment. (C)Both studies are controlled experiments. (D)Both studies are observational studies.
B