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问题 问答题

1673年，英国科学家波义耳将金属放在密闭容器里煅烧，煅烧后他立即打开容器盖进行称量，发现反应后的固体质量增加了。波义耳的实验结果是否违反质量守恒定律？简析原因。

答案

不违反；由于金属在煅烧时会与空气中的氧气反应产生固体氧化物，这个氧化物的质量等于参加反应的的金属和氧气的质量和，导致金属质量增加。（答案合理即可）

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.

On the whole, this passage is positioned to dwell on________.

A．the overall picture of the HDTV sector

B．how the giant TV makers should offer better products

C．a lament over consumers’ inability to use a high-end TV set

D．a criticism of the TV makers for doing nothing about a big problem
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选择题

将生长健壮的枝条剥去一圈树皮后，在枝条上逐渐形成瘤状物位于[ ]

A．伤口上方的树皮

B．伤口下方的树皮

C．伤口上、下方的树皮

D．露出的木质部

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