在20件产品中，有15件一级品，5件二级品，从中任取3件，其中至少有一件为二级品的概率是多少？()
A.A
B.B
C.C
D.D
参考答案：C
解析：
从20件产品中任取三件，其中恰有一件为二级品为事件Ai，恰有两件为二级品为事件A2，三件全为二级品为事件A3，这样，事件A1，A2，A3的概率为
根据题意，事件A1，A2，A3彼此互斥，由互斥事件的概率加法公式，3件产品中至少有1件为二级品的概率是：
| 完形填空：阅读下面的短文，从短文后各题所给的A、B、C、D四个选项中选出能填入空白处的最佳答案。 | ||||
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