6. No senator spoke1 at the convention unless he or she was a Democrat2. No Democrat both spoke at the convention and was a senator

Which one of the following conclusions can be correctly drawn3 from the statements above?

N one but senators spoke at the convention.

No Democrat spoke at the convention.

only Democrats4 spoke at the convention.

No senator spoke at the convention.

Some Democrat senators spoke at the convention.

答案：D

我完全没思路这种题该如何做呢？

第一句说明会议上假如有参议员发言的话，他只能是民主党的参议员，第二句讲发言的人要么是民主党员，要么是参议员。依据第一句，否定掉参议员，只剩民主党了