a “sets” question 求解

freesimens

This is a data sufficiency problem from 《30 days to the GMAT CAT 2nd edition》sets

Susan has selected exactly three crayons, each a different color, from a crayon box. How many crayon colors were represented in the box before her selection?

(1) Exactly four distinct three-crayon color combinations were represented in the box.

(2) Just before Susan's selection, the box contained exactly five crayons.

The answer is C.

I have read the explaination several times,but I still can't understand it.Can anyone give me a clear method or just a translation of the question itself?

Thank you very much!

dhhgh11

S要从盒子中挑出三种不同颜色的粉笔，在她挑之前，盒子里的粉笔一共有多少种颜色？

（1）盒子里有四种不同的三色组合；

（2）S挑之前，盒子里有5支粉笔；

我的意见：本来我是觉得（1）单独就足够了，因为C(n,3)=4=n(n-1)(n-2)/(3*2*1),则n=4；管他有几支粉笔（可能会有相同颜色的粉笔存在...），反正颜色是4种就okay啦...

可是他的答案是C，我又想了想...可能是因为条件（1）并没有说明是挑之前或者挑之后的情况吧...寒！（ETS有这么BT吗？），所以加上2的条件，可以知道，盒子里有4种颜色，至少要有4支粉笔吧...挑之前只有5支，所以（1）所说的是在挑之前的情况...

所以两个条件合起来，可以推出，在S挑之前，有5支粉笔，四种颜色（有两支同色）的粉笔在盒子里...