Rule of Negation is generally applied to assumption questions, but its not limited to these questions only.
Try the opposite of the answer choice. If the argument fails then it means that is the answer. Lets take an example:
Our school district should not spend its money on the new Verbal Advantage reading program. After all, our students get all the reading practice they need by studying history and science.
The argument above depends on which the following assumptions?
(A) The Verbal Advantage program would not help the students learn history and science.
(B) Other reading programs are just as effective but less expensive than the Verbal Advantage program.
(C) The Verbal Advantage program involves only reading practice.
(D) Teaching students history and science is more important than teaching them reading skills.
(E) The students can already read well enough to study history and science.
In the above example if you negate C i.e The Verbal Advantage program DOESN'T involve only the reading practice, then the argument fails. If program invloves many other things then it will be useful and only reading history and science are not sufficient.
Hope this helps.
SAID BUSINESS SCHOOL, OXFORD - MBA CLASS OF 2008