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问题 选择题

打靶3次，事件Ai表示“击中i次”，其中i=0，1，2，3．那么A=A1∪A2∪A3表示的是（　　）

A．全部击中

B．至少有1次击中

C．必然击中

D．击中3次

答案

由题意可得，事件A1、A2、A3，是彼此互斥的事件，且A0∪A1∪A2∪A3 为必然事件，

A=A1∪A2∪A3表示的是打靶三次至少击中一次，

故选：B．

单项选择题

Which of the following statement is closest in meaning to the passage you have just heard a. The WTO ministerial conference held at Cancun is disappointing because the poor countries could not participate in the event. b. The Cancun ministerial meeting was intended to create a more open and equitable trading system. c. The main objective of the Cancun conference was to help the poorest countries in the world to develop their economy. d. Opening up the market in poor countries would have a negative impact on their national economic development.
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单项选择题

THDS-A红外轴温测系统光子探头器件温度正常值范围是（）。

A、（环温-50）±15℃

B、（环温-50）±20℃

C、（环温-50）±25℃

D、（环温-50）±30℃
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