再问天山4－34（TTGWD3－19），搜过了疑问没消除

In Kravonia, the average salary for jobs
requiring a college degree has always been higher than the average salary for
jobs that do not require a degree. 
Current enrollments in Kravonia’s colleges indicate that over the next
four years the percentage of the Kravonian workforce with college degrees will
increase dramatically.  Therefore, the
average salary for all workers in Kravonia is likely to increase over the next
four years. 

Which of the following is an assumption on
which the argument depends?

1. Kravonians
        with more than one college degree earn more, on average, than do
        Kravonians with only one college degree.
2. The
        percentage of Kravonians who attend college in order to earn higher
        salaries is higher now than it was several years ago.
3. The higher
        average salary for jobs requiring a college degree is not due largely to a
        scarcity among the Kravonian workforce of people with a college degree.
4. The
        average salary in Kravonia for jobs that do not require a college degree
        will not increase over the next four years.
5. Few
        members of the Kravonian workforce earned their degrees in other
        countries.

here in this argument ,the author says that since the salary level of person who has college degree is much higher than that of person who has not degree,the salary for all the workforce in country K ,when the number of the predicable graduates from college with degrees will increase dramatically. 

Then the assumption here has two major direction.One is to fill the gap ,the other is to find out the patten ,"not + weaken".

Here in choice C ,we can find that choice C meets the needs of "not + weaken".Now let's express the choice C without "not".The sentence is "The higher average salary for jobs requiring a college degree is due largely to a scarcity among the Kravonian workforce of people with a college degree.".

That means the reason for the fact that salary is so high for the person who has college degree is the amount of such kinds of person is small.And then ,if the amount becomes bigger than ever before ,it's logical to result in the salary level will decrease ,contary to the conclusion made in the argument.

So ,choice C is the best answer.

In choice D,If we do the same as what we did in choice C,relocated the sentence with out "NOT".Then we will found that "The average salary for jobs that do not require a college degree will increase over the next four years".If it is ture and then fortified with average salary for jobs that requires a college degree increase dramtically, the conclusion listed in the argument above will be strengthened not weaken.Then the patten "not + weaken" will be undermined .

So the choice D is not the answer we prefer.