求教一道逻辑题~~

寿司XYZ

In 1973, a remote town first acquired television. Shortly before broadcasts began there, a study was made of children's behavior. A similar study in the same community, after two years of TV, showed that the aggression rate among children of this age had increased by 160%. The conclusion drawn was that TV plays an important role in generating aggressive behavior in children. A second study, covering the same years, was made in two similar communities that had had television for decades. This study showed no change in the aggression rate from 1973 to 1975. The results of the second study:

A) suggest that the prevalence of violent themes in TV programming may be explained by the tendencies toward violence that are deeply-rooted in human nature.
B) indicate that different social groups may react quite differently to similar stimuli.

C) demonstrate that long-term exposure to TV has no more severe effects than short-term exposure.
D) support the conclusion drawn from the first study.
E) disprove the conclusion drawn from the first study.
为什么不选B？？

xp1231

木有讲到different social group是吧。。。。