Never power off before completing write on FLASH for PTN devices. （)

-How often do you go to the cinema？ -().

A: I like cinemas

B: Last week and the week before

C: I've never been to the cinema

D: once a year

To get some idea of the amount of heat the sun ________(1), think about this. If you ________(2)collect all the heat that hits the earth in a two-week period, it would equal the amount of all the other known sources and reserves of energy: wood, coal, and oil. But even these sources of energy depend ________(3) the sun for their formation. For example, a tree ________ (4) certainly never grow and provide fuel in the form. of wood were it not for the sun. Because the sun is so important in the production of all forms of heating fuel, more and more time and money are being spent ________(5) ways to change power from the sun directly into a form. of heat.

1.

A、gives off

B、turns off

C、takes off

D、sets off

2.

A、will

B、could

C、must

D、shall

3.

A、of

B、in

C、on

D、to

4.

A、will

B、must

C、shall

D、would

5.

A、study

B、studied

C、studying

D、being studying

The Earth has a force that pulls things toward itself. We call this force gravity(地心引力). This is something we live with all the time, and we take it for granted and hardly ever think about it. But it is a most important factor in rocket operation and must be overcome if we are to get anywhere in space, or off the ground at all.

Take the throwing of a ball as an example. The harder the ball is thrown, the faster and higher it will go. What is the secret？ It's speed. If we could throw the ball hard enough it would go up and up forever and never come down. The speed at which it would have to be thrown to do this is known as escape speed. Of course, we cannot throw a ball hard enough because the speed required to escape completely from' the Earth's gravity is seven miles per second, or over twenty-five thousand miles per hour.

Once escape speed has been reached by a spacecraft(宇宙飞船), no further power is needed. A rocket aimed at the Moon, for instance, will "coast"(滑行) the rest of the way because the Earth's gravity cannot then pull it back, and there is no air resistance(阻力) in space to slow it down. This "coasting" is known as "free fall". That does not mean the rocket is falling down towards the Earth but that it is traveling freely in space without the aid of power, like a bicycle coasting downhill.

Free fall is an important feature of space travel: it would be impossible to carry enough fuel to provide powered flight all the time.

What is the most important factor for a rocket to escape from the Earth？

A．To travel as fast as it can.

B．To overcome the Earth gravity.

C．To get away from the air resistance.

D．To have strong power in its operation.

Obviously, nuclear power can never be the only (solve) ______ to energy crisis.

A.finding

B.to find

C.having found

D.found

It takes a great deal of power of ______a spaceship into space.

A．elevate

B．launch

C．flourish

D．take off

n power switch of(), and finally power switch of()。