问两道很简单的CR。。求思路

wwc008love

No senator spoke at the convention unless he or she was a Democrat.No democrat both spoke at the convention and was a senator.
Which of the following conclusions can be correctly drawn from the statements above?
A No one but senators spoke at the convention
B No Democrat spoke at the convention
C Only Democrats spoke at the convention
D  No senetor spoke at the convention
E Some Democrat senators spoke at the convention

为啥选D。。求过程。。


Most parents who are generous are good parents,but some self-centered parents are also good parents.Yet all good parents share one characteristic:They are good listeners
If all of the statemetns in the passage are true,which one of the following must also be true?
A all parents who are good listeners are good parents
B Some parents who are good listeners are not good parents
C Most parents who are good listeners are generous
D Some parents who are good listeners are self-centered
E Fewer self-centered parents than generous parents are good listeners
想知道D是怎么推的谢谢

wuqian321

senator 能spoke at the convention 的必要条件是senator is a Democrat。但后面又说No democrat both spoke at the convention and was a senator.即senator不可能是 Democrat。所以选D