下面需要进行根管预备的是 （） A.活髓切断术 B.根管治疗术 C.干髓术

There               a meeting tomorrow afternoon.

A. is going to be          B. is going to have        C. are going to be  

达尔文是19世纪著名的______ 者．

《高层民用建筑设计防火规范》规定，高层建筑地下室、半地下室的安全疏散应符合（）规定。

A.每个防火分区的安全出口不应少于两个

B.当有两个或两个以上防火分区，且相邻防火分区之间的防火墙上设有防火门时，每个防火分区可分别设一个直通室外的安全出口

C.房间面积不超过50平方米，且经常停留人数不超过15人的房间，可设一个门

D.人口密集的厅、室疏散出口总宽度，应按其通过人数每100人不小于1.00m计算

Man first appeared on earth about 2 million years ago. Then he was little more than an animal; but early man had a big advantage over the animals. He had in his brain special groups of nerve cells, not present in animals, that enabled him to invent a language and use it to communicate with his fellow men. 46) This ability to speak was of great value because it allowed men to share ideas, and to plan together, so that tasks impossible for a single person could be successfully undertaken by intelligent team-work. Speech also enabled ideas to be passed on from generation to generation so that the stock of human knowledge slowly increased.
It was this special ability that put men far ahead of other living creatures in the struggle for existence. 47) He mastered darkness first with dim lights and later with brighter and brighter lamps, until he can now make for himself so dazzling a light with an arc lamp that, like the sun, it is too p for his naked eyes.
48) Man found that his own muscles were too weak for the work which he wanted to do; he explored many other forms of power until now he has his hands on the ultimate source of physical energy, the nuclear power. From man’s earliest days the flight of birds has raised his wonder and desire. Why should he not fly as they did Then he began to experiment. At last he learnt how to make the right machines to carry him through the air. Now he can fly faster than sound. Already he has plans for conquering space, and a series of experiments has been completed. 49) It will not be long now before man takes a giant step away from his planet and visits the moon, learning what it is like to have no weight to his body, no upward direction and no downward.
Man, always a wanderer, has to overcome the difficulty of adapting himself to different climates. 50) Fortunately, in spite of having no thick skin or warm fur to protect him, he is peculiarly p compared with other living creatures, most of whom are unable to live far outside the region that suits them best.