what's the difference between "if " and "as long as"?

[Vaok]

The WTO cannot live up to its name _____________ it does not include a country that is home to one fifth of mankind.
A. as long as B. while
C. if D. even though

The suggested answer is C, Why can't A?

Another problem:

_____ modeling business is by no means easy to get into, the good model will always be in demand.
A. While B. Since
C. As D. If

I don't know which is right? It seems B,C,D are all proper.

[Mister Micawber]

.
1-- I think A is fine too, and so is B.
2-- The idea is that it is hard to become a model, but once you do, you will be assured of work. A is the answer.
.
_________________
Native English teacher at Mister Micawber's

[Vaok]

thank you for your answer.

the two problems are from the national entrance examination for college in China.

the given answer of problem 1 is C .
the given answer of problem 2 is D .

Do you mean A,B,C, are proper for problem one, and only A is for problem 2 ?

[Mister Micawber]

.
Bad test. Yes, A, B and C all seem to work in your first problem. I cannot see that 'if' makes any sense at all in your second problem; only A seems right to me.
.
_________________
Native English teacher at Mister Micawber's

[Vaok]

would you please explain the meaning of the word "while" in both of the problems? thanks.

[Mister Micawber]

.
1-- while = at the same time as
2-- while = although
_________________
Native English teacher at Mister Micawber's