gwd-24上一道题，答案是否有误？

katrinaxy520

Q30:

There are 8 books on a shelf, of which 2 are paperbacks and 6 are hardbacks.  How many possible selections of 4 books from this self include at least one paperback?

 

A.     40

B.     45

C.     50

D.     55

E.      60

答案选Ｃ，可是我算的是Ｄ，很简单的一道组合题啊．．．难道是我想错了？

请教ＮＮ！

achine

答案错了

skb1109

C(8,4)-C(6,4)=55 

答案错了~~~

katrinaxy520

谢谢啦！我还以为是自己出了问题．