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
我算的55,但是答案给的C,为啥啊?咋能算出C来呢?
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