为什么说鸟类的原条相当于蛙胚的胚孔？

阅读下面短文，把A-D四个句子填人文中的空缺处使内容完整正确，然后完成第5小题。

     In the world today, all of the people need recreation (消遣). 1______. Everyone has his own way of

relaxing. Perhaps the most popular form (形式) is to take part in sports. There are teams sports，such as

swimming and soccer. 2______. Skating and mountain climbing are the most popular recreation for people

who like to be outdoors.

     Not everyone who enjoys sports likes to take part in them. 3______. So many people like some forms

of indoor recreation, such as watching TV, singing and dancing. 4______. It is important for everyone to

relax from time to time, and enjoy some forms of recreation.

A. It doesn't matter whether we like indoor recreation or take part in outdoor sports

B. We can not work all the time if we are going to keep healthy and enjoy life

C. Many people like watching them on TV or listening to them on the radio

D. There are also individual (个人的) sports, such as swimming and running

5. Which is the best title of the passage?

A. Recreation

B. Relaxing

C. Sports

D. Forms

抗原的特异性主要取决于

A．抗原分子的物理性状
B．抗原分子量的大小
C．抗原的决定簇
D．抗原分子内部结构的复杂性
E．异物性

八大龙王

蒸汽中不凝性气体的存在，会使它的对流传热系数α值（）。

A、降低

B、升高

C、不变

D、都可能

药物半衰期主要取决于其（）

A.剂量

B.消除速率

C.给药途径

D.给药间隔

E.分布容积