问题 单项选择题

下列哪项引起回声影像增强

A.强反射结构
B.传播速度误差
C.Snell定律
D.弱衰减结构
E.以上都正确

答案

参考答案:A

解析: 超声在人体中传播遇到空气(含气脏器和组织)反射强,回波幅度很大,出现亮点、光团。引起回声增强的原因主要有:①均质性的液体中混有许多微气泡;②血液常是无回声的,但是新鲜的出血、新鲜的血肿、静脉内血栓形成时回声增多、增强;③均质性组织发生纤维化、钙化等非均质性改变。

阅读理解

The Aborigines (澳洲土著) have lived in Australia for about 60,000 years. They painted pictures inside caves, and these are the rock paintings that have given us so much information about Aboriginal life. For example, some of the paintings that are about 10,000 years old show men with boomerangs. From this we know that the Aborigines started using boomerangs for hunting at that time. Other pictures show kangaroos, so we know that there were kangaroos at that time.

The Aborigines believed that spirits made people, animals and plants, and that these spirits still live in the earth. For Aborigines, no one can own the earth—the earth belongs to the spirits.

In 1700, there were many Aboriginal groups with a population of 750,000 all over Australia, and there were probably more than 240 different Aboriginal languages. The groups did not have a leader. Instead, things were decided by the older men in a group. People from different groups often travelled hundreds of miles to meet each other.

Aboriginal life changed when an English boat arrived in Australia in 1770. Many Aborigines were killed in the wars that they had with the English. More Europeans came, and they started taking land from the Aborigines. The Europeans also brought new illnesses that killed the Aborigines. The result is that today there are only about 300,000 Aborigines in Australia.

小题1:The Aborigines painted pictures       .

A.on animals’ fur

B.on the land

C.on the tree

D.on the rock小题2:What do you think the Aborigines used boomerangs to do?

A.To paint.

B.To hunt.

C.To fight.

D.To play.小题3:The Aborigines thought        were the most important on the earth.

A.people

B.animals

C.spirits

D.plants小题4:In an Aboriginal group        decided things.

A.the older men

B.the leader

C.the English

D.the Europeans小题5:The number of the Aborigines is small today       .

A.because their living condition was very bad

B.because the English killed a lot of them in the wars

C.because of the new illnesses the Europeans brought them

D.because of the wars and the new illnesses

单项选择题