B is the correct answer, but not for the reasons outlined above.
This is a question from the June 1997 LSAT. This is the last question within section II of the exam. This was, for me, a difficult question, but after diagramming the argument out, it was fairly easy to identify the flaw within the reasoning.
The stimulus states:
"A recent survey showed that 50 percent of people polled believe that elected officials should resign if indicted for a crime, whereas 35 percent believe that elected officials should resign only if they are convicted of a crime. Therefore, more people believe that elected officials should resign if indicted than believe that they should resign if convicted."
Words like "if" and "only if" help to set off sufficient and necessary conditions within conditional reasoning. In this case, the first sentence states "A recent survey showed that 50 percent of people polled believe that elected officials should resign if indicted for a crime" (the "if" sets off a sufficient condition). Rearranging this statement, we can see that "if indicted for a crime (I), then that elected official should resign (R)"
When diagrammed, the statements above should look similar to this:
I--->R
The second sentence states that "35 percent believe that elected officials should resign (R) only if they are convicted of a crime (C)."
The phrase "only if" sets off a necessary condition. The diagram of this statement should look as follows:
R--->C
The conclusion of the argument says "Therefore, more people believe that elected officials should resign if indicted than believe that they should resign if convicted."
This (flawed) conditional statement would be diagrammed as follows:
Therefore, more people believe that I--->R than believe C--->R; or more simply I--->R, C--->R
The sufficient and necessary (required) conditions have been confused. A sound conclusion based on these statements would read:
"Therefore, more people believe that elected officials should resign if indicted than believe that they should resign only if convicted."
The correct diagram of these statements would look like this:
I--->R, R--->C
In short, the conclusion confuses a sufficient condition with a necessary (required) condition, as reflected in answer choice B.