骨巨细胞瘤X线片表现特点是（） A.骨干中心透明影中有钙化 B.骨端膨胀破坏，呈

good friend always gives you a helping hand ________ you are in trouble.[ ]

A. when

B. before

C. until

D. though

(一)

A公司应邀参加氮制造厂合成压缩工段技改工程投标，招标书说明，以工期安排最短、最合理为中标主要条件。A公司技术部门依据招标书指出的工程内容编制了网络计划(见下图)。

附加说明：

1．配管包括机泵本体配管25d，塔器本体配管20d，塔机间连接配管15d。

2．试运行包含空负荷单机和联动试运转，考虑不可预见因素较多，计划安排15d的试运行时间。

A公司总工程师审核认为网络图不符合最短工期要约，退回重编，要求附加说明。经修改重编网络图，A公司最后中标。

施工中无损检测发现甲供货方提供的高压管件焊缝存在缺陷，退货重供，延误施工10d，A公司为保证总工期不变，加大投入，实施加班作业，最终如期完工。为此，A公司向业主发出索赔意向书。

问题

以不压缩各工序的工作时间为前提条件，画出重编的网络计划图。工期可缩短多少天？以节点符号表示出关键线路。并以重编的网络计划为前提，附加说明如何再进一步缩短工期？

读黄土高原略图，完成下列问题：

（1）山脉A是__________，该山脉以东是___________（地形区），是_________省。B 是___________________；C是_____________。城市①_________，②_________，③___________，④___________。

（2）黄土高原主要分布在__________、________两省，该地区面临的生态环境是______________，形成的自然原因是___________________________________________________；人为原因是_______________________________________________。（各写两条）

（3）该地区在地形、气候和农业生产方面均表现出明显的过渡性，请你试举两例说明：①____________________________________________________；②_________________________________________________。

（4）综合治理黄土高原采取的生物措施是___________________________________________________________；工程措施是____________________________________________。

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.

计算机网络是网络结点和物理信道的集合，一般由两部分组成：（）。