Study 1 Researchers studied the effect of eating nuts on cholesterol levels. 600 volunteers were divided into two groups. One group was required to consume a fixed quantity of nuts every day for five weeks. The other group ate no nuts during the same period. Study 2 Researchers studied the effect of eating chocolates on incidence of depression. 2,300 participants were asked to fill out questionnaires to determine if they were depressed. Volunteers were also asked to state the number of chocolate bars they ate each week. Which statement correctly describes the two studies? A) Both studies were experimental studies. B) Both studies were observational studies. C) Either study could be considered as observational. D) Study 1 was an experimental study and Study 2 was an observational study.