LSAT-18-2-7

ztlbox

7. All psychiatrists are doctors. Only psychiatrists were invited to the conference. All who were invited to the conference stayed at the Hefford Hotel. Therefore, only psychiatrists stayed at the Hefford Hotel.

Which one of the following statements, if added as a premise to the argument, would make the conclusion valid?

(A) Only those who were invited to the conference stayed at the Hefford Hotel.

(B) All who were invited to the conference were psychiatrists.

(C) All psychiatrists were invited to the conference.

(D) No one who was invited to the conference failed to stay at the Hefford Hotel.

(E) Only doctors stayed at the Hefford Hotel.

这道题不知有没有人问过，帮忙看一下怎么推的

lawyer_1

这种题就是画圈圈：有个规律。All A is B。A 在B圈内。Only A is B，则相反，B在A圈内。

Bensontuo

ztlbox 发表于 2004-8-23 08:45
7. All psychiatrists are doctors. Only psychiatrists were invited to the conference. All who were in ...

All P ---> D

C --- > P

All C ----> H
----------------
C ---> P ---> D
----------------
So H ---> P

So, it must be C ---> H ---> P ---> D

SO, All H must be D, in the other word, Only doctor would be in H hotel.

A. H ---> C. Mistaken Reverse.

B. C ---> P. ( Premises Booster )

C. P ---> C. ( Mistetaken Reverse )

D. C ---> No ( No ) H => C ---> H ( Premises Booster )

E. H ---> D ( Must be true ). Correct answer.