问题 问答题 简答题

双晶的定义、双晶要素。

答案

参考答案:

双晶:是同种晶体的规则连生,相邻的两个单晶体间互成镜像关系,或其中一个单晶体旋转1800以后与另一个重合或平行。

双晶要素:

(1)双晶面:为一假想的平面,可使构成双晶的两个单体中的一个通过它的反映变换后与另一个单体重合或平行;

(2)双晶轴:为一假想直线,双晶中一单体围绕它旋转一定角度后(一般都为180°),可与另一单体重合或平行。

选择题
阅读理解

“Choo, Choo!” Here comes the Chunnel train. Get aboard if you want to learn more about this underground transportation system. This is an unusual form of transportation, because it is a tunnel that trains travel through and not an actual form of transportation.

The Chunnel is actually the English nickname for the Channel Tunnel. In French, it is called le tunnel sous la Manche. It is a rail tunnel beneath the English Channel at the Straits of Dover. It connects Cheriton in Kent, England with Sangatte in northern France. It is the second longest rail tunnel in the world.

Did you know that the British and the French had a race whi1e they were building the Chunnel? The race was to see who could get to the middle of the tunnel first. The British won by a little bit. It took 15,000 workers over seven years to dig the tunnel. The tunnel was finished in 1994.

The completed Chunnel cost about $ 21 billion. But it all paid off, because it became very popular, very quick. Millions of people use it. Now it is getting even more popular.

There are three complete tunnels in the Chunnel. The two outside ones are the passenger trains. The small inner one is a guidance train. The guidance train is not used for transportation. Each track is exactly parallel to each other.

There are four different train systems in the Chunnel. The Eurostar is a high speed passenger service that connects London, Paris, Brussels, and Lille. The Eurotunnel shuttle is a rail ferry service. These shuttles carry cars. These are railcars that allow drivers to drive their vehicles on and off. There are also two Eurotunnel goods service trains.

Now you know more about the Chunnel. Everybody off, this is the last stop.

小题1:The Channel Tunnel links ______ with _______.

A.Dover; Kent

B.London; Paris

C.Lille; Brussels

D.Cheriton; Sangatte小题2:Which of the following shows the structure of the tunnels in the Chunnel?

小题3:The Eurotunnel shuttle is intended to carry _________.

A.passengers

B.drivers and their vehicles

C.goods

D.staff members of the Chunnel小题4:The text can most probably be __________.

A.found in a textbook

B.read in a magazine

C.broadcast on a train

D.heard in a railway station