1. A scientist planted two groups of plants under identical conditions of light, temperature, humidity, and moisture. Every day he would play sound effects of thunderstorms to one of the group of plants and sounds of city traffic for the other. The group of which he played thunderstorm all died within a few weeks, but the other group thrived during the experiment. He therefore concluded that the sound of city traffic is more effective for help plants grow than is the sound of thunderstorms. Ø Which of the following, if true, would most seriously weaken the scientist’s conclusion
A．A. The scientist put difference varieties of plants in each group.
B．B. The light affecting the plants changed according to the time of day
C．C. The plants in the group for which he played city traffic sounds died several weeks after the experiment.
D．D. The plants were all purchased at the same time.
E．E. The plants in the group for which he played city traffic sounds required more water than the scientist actually gave them.