以下为baby姐姐的解答,感觉很简明很清晰,学习之~~ The interstitial nucleus. 这题之前做过,选E. "关于B选项第一感觉总是提供它因,想了好久才想明白" READ LITERALLY! "Many male cats who contract disease X also contract disease Z" this provides a coincidence. carefully note that coincidence does not mean causal relationship. "the cause of which is unknown" Okay, so here it says, Z has NO known causal relationship with X. To sum up, choice B is talking about a new stuff Z, which has no known causal relationship with our focus. In other words, it's out of scope.