继续请教（3）

liflyy

9。masterpieces of literature are "intertextual", that is, they tend to be written in response not to reality but to other works of literature. to the extent that a writing is tertextual, it becomes clouded as a mirror of social reality.
Q: support
A: literary masterpieces of the past are suspect as sources of information about the social reality of the past.

不明白？

10。 no ambitious politician will challenge an elected public official running for reelection unless that official appears vulnerable. nonetheless, elected public officials who do not appear vulnerable as they attempt to win reelection rarely run unopposed.
A: some elected official running for reelection are challenged by people who are not ambicious politicians.
这道题是怎样推的呢？

11。recent estimates predict that between 1982 and 1995 the greatest increase in the number of people employed will be in the category of low-paying service occupations. this category, however, will not increase its share of total employment, whereas the category of high-paying service occupations will increase its share.
Q: conclusion drawn
A: (a) 1982 more people were working in low-paying service occupations than were working in high-paying service occupations.
   (b) 1995 more people will be working in high-paying service occupations than will be working in low-paying service occupations.

why a not b?哪位大虾从数学方面解释一下这道题。