氨是一种重要的化工产品，其化学式为______，具有______气味，密度比空气

一张椅子245元，办公桌的价钱比椅子贵300元。

（1）一张办公桌的价钱是多少元？

（2）买一张办公桌和一把椅子一共要多少元？

阅读下面短文 ， 根据题目要求及上下文语境填词 ，使短文正确、通顺 。每空一词 。（ 每小题1分 ，共10分 ）

Environmental pollution is one of the most serious problems. Pollution has a bad

     小题1:  / ′Influəns/ on our life.

With the d  小题2:  of modern industry, environmental pollution is increasing quickly. More and more factories      小题3:  (生产，制造) waste gas . The air is becoming dirtier and 

    小题4:  ，and it affects so many people’s health. Air pollution can cause b   小题5:   _ problems and even cancer.

The increase in the number of industries has caused the water problems, too. There are more and more chemical factories   小题6:   waste water into rivers and lakes. Water pollution kills fishes and other living things.

Noise pollution is also h   小题7: to people’s health. It       小题8:   (打扰) people and many people can’t sleep well at night . It can make people     小题9:    /def/ and they may have hearing loss.

I hope the government can take      小题10:( 措 施  ) to protect our environment in many ways .

为验证Zn、Cu、Ag的金属活动性顺序，下列实验方案中合理的是

A．将Zn、Cu、Ag分别放入稀盐酸中

B．将Cu、Ag分别放入ZnCl₂溶液中

C．将Zn、Cu、Ag分别放入AgNO_3­溶液中

D．将Zn放入CuCl₂溶液中，将Cu放入AgNO₃溶液中

影响生物膜相变的因素有那些？他们是如何对生物膜的相变影响的？

汽轮机在正常停机过程中，不会发生超速事故。