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问题 单项选择题

上杆前，应先分清相、零线，选好工作位置。断开导线时，应先（）。搭接导线时，顺序应相反。

A.断开零线，后断开相线；

B.断开相线，后断开零线；

C.先断开火线，后断开地线；

D.先断近端。后断远端。

答案

参考答案：B

单项选择题

A total of 4.6 million digital televisions have been sold, and the sales of HDTV sets have quadrupled since last year. Consumers have bought HDTVs to play their DVDs and to have clearer pictures and wide screens. Only a small percentage of the people who have purchased HDTVs, however, have actually hooked their TVs up to receive high-definition television digital signals. Perhaps television viewers are having trouble keeping up with the changes in technology. Even the manufacturers of HDTVs, like Mitsubishi, Thomson Multimedia, Sony, and Samsung seem to have a tough time learning how to make their sets work with the various digital TV formats because little standardization has been required or implemented in the industry.

Some of the HDTVs weigh over 200 lbs., and a variety of retailers offer a delivery service to the buyer’s home to help install the heavy sets. This is known as a white-glove service and usually comes with an extra fee. After HDTV purchasers get their sets home and hook them up, they will still need to work to get the digital signals to their systems. Most of the industry’s cable providers do not yet offer high~definition programing, and only about 15% of commercial television stations have switched over to even the lowest improved digital pictures. Worse yet, viewers may need to install antenna before they can even get the digital signals to their new HDTV sets. Another frustration for home-theater seekers is that the current HDTV sets allow owners only to watch high-definition programs, not to record them.

According to the first sentence, the sales of HDTV sets since last year, by the time when this article was written, had reached ().

A. 4.6 million

B. 9.2 million

C. 18.4 million

D. I do not know how many
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选择题
点A（2，4）关于x轴对称的点的坐标为（　　）
A．（4，2）B．（2，-4）C．（-2，4）D．（-2，-4）
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