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In the future, people may travel to Mars (火星) by water-powered spaceship! Today's spaceships are fine for getting things into space, but they are not so good at travelling long distances. These spaceships burn chemical fuels (燃料) and they are very expensive. Scientists say that a water-powered spaceship could make the trip to Mars much cheaper. The idea is just in the planning stages now, but scientists think such a spaceship could be developed soon.

The key to the water-powered spaceship is the engine (发动机). Regular engines push spaceships by burning fuel. The water engine will use steam, created by solar panels (太阳能板) that heat water to a high temperature. Of course, the spaceship will have to carry a lot of water for the long trip to Mars.

Today's spaceships could not carry that much water. But scientists think that a spaceship blown up like a balloon will be able to.

One US company has already developed a spaceship like this. These spaceships are made of a strong material. Two of them have already been sent up into space, using rockets and then later filled with air. "Balloon" spaceships could be very large and carry enough water for a long trip. With the "Balloon" spaceships, enough water could be carried to power the engines and grow food during the trip. And the people on the spaceship might even get to take a hot bath!

Scientists say the biggest advantage of such a spaceship would be cost. The "Balloon" spaceship uses water to push it through space and costs about one thirtieth of a normal spaceship. Such savings naturally encourage continued research into balloon spaceships and water engines. If these scientists are correct, we may soon be on our way to Mars in a spaceship powered by water.

1．Which sentence best describes the main idea of the passage above?

A．The key to the water-powered spaceship is the engine.

B．In the future, people may travel to Mars by water-powered spaceship.

C．One US company has already developed a spaceship like this.

D．Scientists say the biggest advantage of such a spaceship would be cost.

2．What do you think is omitted (省略) at the end of the underlined sentence?

A．use steam	B．push spaceships
C．heat water	D．carry that much water

3．Besides growing food, what else might astronauts do with the rest of the water?

A．Take a hot bath.	B．Freeze dangerous things.
C．Blow up a balloon.	D．Change the surface of Mars.

4．On which website can we probably read this passage?

A．www. freedictionary. com/power	B．www. mooc. cn/music
C．www. chinadaily. com. cn/culture	D．www. space. com/spaceflight