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问题 填空题

用下列序号填空： ①烧杯  ②试管  ③胶头滴管  ④燃烧匙  ⑤蒸发  ⑥过滤  ⑦搅拌  ⑧量取， 将食盐放入水中，为使其尽快溶解可采用的操作 _________ ；能直接加热的玻璃仪器 _________ ； 吸取或滴加少量液体的仪器 _________ ；取用6.8mL某溶液的操作 _________ ．

答案

⑦；②；③；⑧

单项选择题

(B)

You can tell the age of a tree by counting its ring. But these records of a tree’s life really say a lot more. Scientists are using tree ring to learn what’s been happening on the sun’s surface for the last ten thousand years. Each ring represents a year of growth. As the tree grows, it adds a layer to its trunk, taking up chemical elements from the air. By looking at elements in the rings from a certain years, scientists can tell what elements were in the air that year. Dr. Stevenson is analyzing one element, carbon-14, in ring from both living and dead tree. Some ring go back almost ten thousand year to the end of the Ice Age. When Stevenson followed the carbon-14 levels changed with the intensity of solar burning. You see, the sun has cycles. Sometimes it bums fiercely, and at other times it is relatively calm. During the sun’s violent periods, it throw off charged particles in fast moving streams called "solar winds". The particularly interfere with the formation of carbon-14 on earth. When there is more solar wind activity, less carbon-14 is produced. Ten thousand years of tree ring show that the carbon-14 level rises and falls about every 420 years. The scientists concluded that solar wind activity must follow the same cycle.

The underlined phrase "throw off" probably means（）

A. give away

B. cast

C. send for

D. get rid of
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单项选择题

一个计算机系统有三个I/O通道：
(1)字节多路通道，带有传输速率为1.2KB/s的CRT终端5台，传输速率为7.5KB/s的打印机2台；
(2)选择通道，带有传输速率为800KB/s的温盘一台，
(3)数组多路通道，带传输速率为800KB/s及600KB/s的磁盘各一台，则通道的最大速率为______KB/s。

A．1821

B．2421

C．3221

D．1621
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