下午1:55 4月21日周四 * 77% •.. 37. An agricultural scientist wanted to compare the effect of a new fertilizer to that of three older fertilizers-X, Y, and Z-on the growth of vegetables typically grown in...

Extracted text: 下午1:55 4月21日周四 * 77% •.. 37. An agricultural scientist wanted to compare the effect of a new fertilizer to that of three older fertilizers-X, Y, and Z-on the growth of vegetables typically grown in small gardens. Two hundred green bean seedlings were individually planted in identical pots and randomly assigned to one of four groups of 50 each. Seedlings in one group were given the new fertilizer, and the three remaining groups of seedlings were given fertilizers X, Y, or Z, respectively. At the end of four weeks, all seedlings were dried and weighed. The scientist found that the mean weight of the seedlings in the group given the new fertilizer was significantly greater than the mean weights of seedlings in the other three groups. The scientist concluded that the new fertilizer was more effective than the other fertilizers for all vegetables. Why is the scientist’s conclusion not appropriate? (A) The study was observational, so cause and effect cannot be concluded. (B) The study was observational, so no replication was used in the study. (C) The experiment only included green beans, so the results cannot be generalized to all vegetables. (D) The experiment did not group the seedlings into blocks by the variety of beans. (E) The experiment lacked a control group that did not use any fertilizer.