搜题请搜索小程序“爱下问搜题”
问题 选择题
已知1g火箭燃料肼（N2H4）气体燃烧生成N2和H2O（g）时，放出16.7kJ的热量，则该反应的热化学方程式正确的是（   ）

A．N2H4+O2=N2+2H2O△H=-534.4kJ/mol

B．N2H4（g）+O2（g）=N2（g）+2H2O（g）△H=-534.4kJ/mol

C．N2H4（g）+O2（g）=N2（g）+2H2O（g）△H=+534.4kJ/mol

D．N2H4（g）+O2（g）=N2（g）+H2O（g）△H=-16.7kJ/mol

答案

答案：B

补全对话，情景问答
根据对话内容及方框中所给的句子补全对话.其中有一项是多余的.
A. Have you cleaned the windows yet?
B. Have you cleaned the blackboard yet?
C. Who is on duty today?
D. Have you carried some water yet?
E. Have you watered the flowers?
F. When did you do it?
A: Good morning.  Xiao Jing. __1__.
B: I am.  Mr Zhang.
A: __2__.
B: Yes, I cleaned it ten minutes ago.
A: __3__.
B: Yes, I did it half an hour ago.
A: __4__.
B: Yes. Look, they are as clean as mirrors.
A: So they are! __5__.
B: Yes, some boys helped me to get water from the well.
A: Very good, thank you, Xiang Jing.  Now, let's begin our class.
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单项选择题

我国蔬菜栽培主要以（）作肥料，因此肠道致病菌和寄生虫卵污染很严重。

A、无机肥

B、农药

C、化肥

D、人畜粪便
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