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问题 选择题

下列物质中，属于单质的是（　　）

A．煤

B．干冰

C．氢气

D．氯酸钾

答案

A、煤是混合物，故错误．

B、干冰是二氧化碳的固体，是氧化物，故错误．

C、氢气是一种元素组成的纯净物是单质，故正确．

D、氯酸钾是三种元素组成的纯净物，是化合物，故错误．

故选C

补全对话，情景问答

补全对话。

Clark: What events do you ____1____ at your school?

David: We have an English Speech Contest each year.

Clark: ____2____ is it?

David: It's March 5th.

Clark: Do you have ___3_____ Art Festival?

David: Yes. It's March 17th. ___4___ we have a basketball game on March 10th.

Clark: When is your School Trip?

David: It's April 6th.

Clark: Is Linda's birthday ___5___in April?

David: Yes. It's April 18th.

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单项选择题

在程序运行期间，如果拖动滚动条上的滚动块，则触发的滚动条事件是______ 。

A．Move

B．Change

C．Scroll

D．GetFocus
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