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问题 单项选择题

某种产品的寿命服从参数为λ的指数分布，即假定其平均寿命为4000h，则

要达到可靠度为90%的可靠寿命约为（）h。

A．24

B．18

C．42

D．81

答案

参考答案：C

解析：

由可靠度公式R(t)=e-0.0025tln0.9，故。

句型转换

将下列各句变成否定句和一般疑问句并作简短的肯定、否定回答。

1. She does her homework every day.

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2. He can make some cakes 

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3. There are a lot of people in the room.

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4. I think they are from the USA.

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5. Kevin is reading an English book now.

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6. They have red pens and blue pencils. 

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单项选择题 A1/A2型题

小儿硬膜外阻滞时，利多卡因宜用的浓度和剂量是（）

A.0.7%～1.5%，1～2mg/kg

B.1%～2%，4～5mg/kg

C.0.7%～1.5%，8～10mg/kg

D.1.5%～2%，5～7mg/kg

E.2%，10mg/kg
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