问题 选择题

下列实验操作正确的是

答案

答案:B

题目分析:A、取用液体时:①试剂瓶瓶口要紧挨试管口,防止液体流出;②标签向着手心,防止液体流出腐蚀标签;③瓶塞没有倒放桌面上,可能会污染瓶塞,从而污染药品,故A错误;B、在检验装置的气密性时,利用的是装置内气体的压强改变,有气泡冒出时,说明装置气密性良好,否则气密性不好,操作正确,故B正确;C、加入固体和液体时,要先加入固体,再加液体,故C错误;D、做铁在氧气中燃烧的实验时,为防止生成物熔化溅落下来,使瓶底炸裂,集气瓶底要装少量的水或铺一层细沙,故图示操作错误,答案选D。

阅读理解

The planets aren’t the only wanderers(漫游者) of the sky. There’re some things even farther and longer. Long after people were no longer afraid of planets, they still thought the comets(彗星) were bad objects that traveled in the sky. They were afraid that the comets would suddenly land on the earth and hurt them.

But, in fact, even if a comet did hit the earth, nothing much happened. A comet is really a harmless (无害的)thing.

Comets have round heads and long tails , and they are very bright. Sometimes they look like heads with long hair flying with them. That’s why they’re called comets. Comet means long-haired.

Like the stars and planets, comets are far away. But we can know its size. The head of a small comet is as wide as the Pacific Ocean. And a big comet’s head is ten times as big as the earth. Its tail is millions of kilometers long. Then why wouldn’t the great big thing hurt us if it hit the earth? Because it isn’t solid. It’s thin like cloud. Its tail is nothing but bright gas. And its head is made of small pieces and they could not hurt the earth.

Some comets can be seen for a few months. Then they go away. Some of them come back in a certain number of years. Some are never seen again.

Perhaps these comets that never return have broken into pieces. For some astronomers  think that shooting stars(流星) are pieces of broken comets.

小题1:People were afraid ________.

A.comets are different from planets

B.comets travel in the sky

C.comets are much bigger than the earth

D.comets could hit the earth小题2:Comets have long tail like ________, so we call them comets.

A.long hair

B.round heads

C.round dishes

D.wide wings小题3:From the passage we know the tails of comets are made of  ________.

A.water

B.solid

C.gas

D.small stones小题4:The underlined word “astronomers” may mean ________ in Chinese.

A.心理学家

B.艺术家

C.天文学家

D.考古专家小题5:Which of the following is TRUE ?

A.A comet is a kind of planets.

B.Comets are all ten times as big as the earth.

C.People can hardly see comets.

D.Shooting stars may come from the broken comets.

选择题