PLC的输入、输出接口电路一般采用（）来传递信号，这样可抑制外部干扰源对PLC的影响

阅读理解。

     HAVE you ever thought of being able to fly around the world in a few hours though it is about 40,000

kilometers? Now, maybe you can. Last Saturday, the American X-43A airplane made its first flight. It

reached a speed of 8,000 kilometers an hour. This makes it the fastest plane in the world. X-43A is only

three to four meters long,but it's very heavy: it weights 1,270 kilos.

     HOW old cart an insect be? 400 million years! Last Wednesday, scientists found the world's oldest insect

fossil (化石) in Britain. The fossil shows that the body of the insect was as big as a piece of rice and had

wings (翅膀). In the past, people thought the earliest insect was 380 million years old.

    THERE will be a new "star" in the sky soon. China plans to send a satellite (卫星) into space by September

2009. It will stay in space for one year. It will go around the moon and take pictures. It must be very

expensive, right? That's for sure-1.4 billion yuan! 

    Yuan Longping, the father of hybrid rice (杂交水稻), won the World Food Prize on Monday. Yuan

developed the world's first popular and widely grown hybrid rice. Hybrid rice plants can make more rice

than the ones people grew before.

1.If the X-43A goes round the earth, it will take about ______ hours to finish the trip. [ ]

A.3

B.5

C.8

D.12

2.The newly-found insect fossil showed that the earliest insect was ______ years older than believed. [ ]

A.10 million

B.400 million

C.20 million

D.380 million

3.Which of the following about the new star is NOT true? [ ]

A.It will go into space by September 2008.

B.It will stay in space for twelve months.

C.It costs a lot.

D.It will go around the moon.

4.Yuan Longping won the World's Food Prize because he ______. [ ]

A.is the father of his children.

B.likes to eat hybrid rice.

C.developed the world's first popular and widely grown hybrid rice.

D.grows more rice than others.

5.The above paragraphs are taken from ______. [ ]

A.a story

B.an advertisement

C.an explaining writing

D.a newspaper

闸板阀有何特点？

利用分子的知识解释：

（1）水在夏天比在冬天蒸发得快，说明______．

（2）水受热变成水蒸气，体积变大，说明______．

如图所示，小球在竖直向下的力F作用下，将竖直轻弹簧压缩，若将力F撤去，小球将向上弹起并离开弹簧，直到速度为零时为止，则小球在上升过程中

A．小球的机械能守恒

B．弹性势能为零时，小球动能最大

C．小球在刚离开弹簧时动能最大

D．小球在刚离开弹簧时机械能最大

帕金森病的主要治疗方法有（）

A.言语训练

B.步态训练

C.免疫抑制剂

D.多巴胺替代药

E.主动关节活动