信源编码和信道编码有什么区别？为什么要进行信道编码？

从设计规定的研究对象中对随机抽出的一部分进行调查，称为（）

A.普查

B.队列研究

C.病例对照研究

D.抽样调查

E.理论流行病学研究

易变色的中药是（）。

A.款冬花

B.厚朴

C.人参

D.甘草

关于"星形细胞瘤"，下列描述哪项不对（）。

A.Ⅰ级CT平扫为边缘清楚低密度灶

B.Ⅱ～Ⅳ级CT平扫可为等、高混杂密度

C.小儿多发生于小脑

D.成人以脑干居多

E.肿瘤强化程度与恶性程度成正比

记载酒的最早文字是商代甲骨文。（）

Passage One

In many countries today, laws protect wildlife. In India the need for such protection was realized centuries ago.

About 300 B. C. an Indian writer described forests that were somewhat like national parks today. The killing of game animals was carefully governed. Some animals were fully protected. Within the forest, nobody was allowed to cut trees, burn wood, or trap animals for their furs. Animals that became dangerous to human visitors were trapped or killed outside the park, so that other animals would not become uneasy.

The need for wildlife protection is greater now than ever before. About a thousand sorts of animals are in danger of extinction, and the speed at which they are being destroyed has been putting on. With mammals, for example, the speed of extinction is now about one sort every year; from A. D. 1 to 1800, the speed was about one sort ever), fifty years. Everywhere, men are trying to solve the problem of saving wildlife while caring for the world’s growing population.

According to the report, men trying to save wildlife are thinking about（）as well.

A．the animals in national parks

B．stricter laws against hunting

C．the trees in the forests

D．the needs of people