下列关于直丝弓矫治器的矫治特点，错误的是（） A.强调托槽位置的精确 B.高弹性弓丝

若等腰三角形两边长分别是4cm、5cm，则这个三角形的周长是______．

阅读理解。

     There was great excitement on the planet of Venus (金星) this week. For the first time Venusian scientists

managed to land a satellite on the planet Earth, and it has been sending back signals as well as photographs ever

since.

     The satellite was directed into an area known as Manhattan (named after the great Venusian astronomer

Prof. Manhattan, who first discovered it with his telescope 20000 light years ago).

     Because of excellent weather conditions and extremely strong signals, Venusian scientists were able to get

valuable information as to feasibility (可行性) of a manned flying saucer (碟) landing on Earth. A press

conference was held at the Venus Institute of Technology.

     "We have come to the conclusion, based on last week's satellite landing," Prof. Zog said, "that there is no

life on Earth."

     "How do you know this?" the science reporter of the Venus Evening Star asked.

     "For one thing, Earth's surface in the area of Manhattan is made up of solid concrete and nothing can grow

there. For another, the atmosphere is filled with carbon monoxide (一氧化碳) and other deadly gases and

nobody could possibly breathe this air and survive."

     "What does this mean as far as our flying saucer program is concerned?"

     "We shall have to take our own oxygen with us, which means a much heavier flying saucer than originally

planned."

     "Are there any other dangers that you discovered in your studies?"

     "Take a look at this photo. You see this dark black cloud hovering (盘旋) over the surface of Earth? We

don't know what it is made of, but it could give us a lot of trouble and we shall have further tests before we

send a Venus Being there."

     "Over here you will notice what seems to be a river, but the satellite findings indicates it is polluted and the

water is unfit to drink. This means we shall have to carry our own water, which will add even greater weight

to the saucer."

     "If all you say is true, won't this set back the flying saucer program several years?"

     "Yes, but we shall continue as soon as the Grubstart gives us the added funds." Prof. Zog replied.

1. During the week of great excitement the Venusian scientists succeeded in getting important information as

    to _____.

A. the feasibility of landing a satellite on Earth

B. the possibility of making a first-rate flying saucer

C. the feasibility of sending a Venus Being to Earth

D. the possibility of directing a flying saucer into Manhattan

2. According to Prof. Zog, the Venusians will have to take their own oxygen with them when they carry out

    their flying saucer program because _____.

A. they need it in their way to the planet of Earth

B. the Earth's atmosphere is filled with deadly gases

C. there is a low level of oxygen for Venusians

D. there is no air on the planet of Earth

3. The "dark black cloud" on the photo refers to _____.

A. the polluted air hovering over the surface of Earth

B. the mass of tiny drops of water floating above Earth

C. the mass of small things moving through the air

D. the dark clouds gathering before a storm breaks

4. The author wishes to call our attention to the fact that _____.

A. that modern man has polluted his environment to such an extend that he might destroy himself if he went

    on like this

B. that there is a point in spending billions to land a flying saucer on Earth

C. that pollution has become so serous a problem on Earth that even Venusians find life there unbearable.

D. that it is difficult if not altogether impossible, to land a manned flying saucer on Earth

影响冲压件工艺性的主要因素有：冲压件的外形、尺寸、精度及（）等。

触发脉冲信号应有一定的宽度，脉冲前沿要陡。电感性负载一般是1ms，相当于50Hz正弦波的( )。

A．360°

B．180°

C．90°

D．18°

人的心理的变化过程包括( )。

A．萌芽

B．发生

C．成熟

D．衰老