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问题 单项选择题

参数估计是依据样本信息推断未知的（）。

A.总体参数

B.样本参数

C.统计量

D.样本分布

答案

参考答案：A

解析：参数估计是依据样本信息推断未知的总体参数，而假设检验是先对总体参数或分布形式提出某种假设，然后利用样本信息和相关统计量的分布特征去检验这个假定，做出是否拒绝原来假设的结论。

选择题

The eighteenth and nineteenth centuries _____ the widespread use of electricity and the birth of the steam engine , leading to the development of factories and cities.

A．watched

B．observed

C．saw

D．showed
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单项选择题

More and more residences, businesses, and even government agencies are using telephone answering machines to take messages or give information or instructions. Sometimes these machines give (1) instructions, or play messages that are difficult to understand. If you (2) telephone calls, you need to be ready to respond when you get a (3)

The most common machine is the (4) used in residence. If you call a home (5) there is a telephone answering machine (6) you will hear several rings and then a recorded message that (7) says something like this: "Hello. We can’t come to the (8) right now. If you want us to call you back, please leave your name and number after the beep." Then you will hear a "beep", (9) is a brief, high-pitched (10) . After the beep, you can say who you are, whom you want to speak to, and what number the person should call to (11) you, or you can leave a (12) . Some telephone answering machines record for only 20 or 30 seconds after the beep, (13) you must respond quickly.

Some large businesses and government agencies are using telephone answering machines to provide information on (14) about which they receive a large volume of (15) . Generally speaking, using these systems (16) you to have a touch-tone phone ( a phone with buttons rather than a rotary dial). The voice on the machine will tell you to (17) a certain button on your telephone if you want information on Topic A, another button for Topic B, and so on. You listen (18) you hear the topic you want to learn about, and then you push the (19) button. Immediately after making your (20) , you will hear a recorded message on the topic.

7（）

A．so

B．therefore

C．although

D．thus
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