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问题 选择题

硅藻土的化学成分主要是SiO2，含有少量的Al2O3、Fe2O3等和有机质。硅藻土是

A．氧化物

B．单质

C．化合物

D．混合物

答案

答案：D

题目分析：因为硅藻土的化学成分主要是SiO2，含有少量的Al2O3、Fe2O3等和有机质，说明有多种物质组成，顾属于混合物，答案选择D.

写作题

书面表达。

     国内某家英文报社设有一个求助信箱。请根据一份学生现状调查中列出的信息，以初三学生王磊

的名义给报社写一封80词左右的英文信。

     信的开头和结尾均以给出。 

                                 

参考词汇：过重的负担 overload;   压力 pressure;   期望 expectation

Dear Dr. Helper,

     I am a Junior student. I am now in great need of your help                                                   

                                                                                                                                           

                                                                                                                                           

                                                                                                                                           

I write this letter only to wish I could have someone to talk to. I'm looking forward to your advice.

                                                                                                                       Your sincerely,

                                                                                                                       Wang Lei

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单项选择题

气相色谱分析法定性依据是（）

A.死时间

B.色谱峰高

C.峰面积

D.色谱峰宽

E.保留时间
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