题目内容：

Satellites play big roles in modern life. Some look downward to monitor environmental conditions on Earth.Others look outward in search of major solar flares(耀斑) that can trouble the transmission(传送) of electrical power to homes and businesses. Some spy on our enemies. Others relay communications around the globe. But all of these million-dollar wonders of technology can be knocked out by a collision with space junk ---debris (碎片 )from satellites and other earthly technology orbiting high above the planet. Now,a teen from Jordan has designed a satellite to chase down space junk , collect it and then deal with it.

Even bits of space junk as small as dots of paint pose a threat , says Dana. That's because this debris orbits our planet at speeds up to some 28,200 kilometers per hour. Such high speed explains why tiny paint dots have damaged the windshields of space shuttles so badly that they needed to be replaced.

Researchers have come up with many ideas for getting rid of space junk. Some have suggested vaporizing(蒸发) small bits with lasers. Others have proposed launching satellites to collect the debris. Dana's design falls into this category.

Here's how hers would work : A radar system aboard the satellite would scan and find a piece of space junk.Then,thrusters(推进器)would change the satellite's orbit so that it could chase down the errant object. As the satellite closed in on its prey, cameras would keep it on target.

At the last minute,a door that leads to a container would open. This container needs to be strong so that it doesn't break apart when the satellite swallows the space junk,Dana explains. Finally,when the trash container was full,it would be lowered toward the earth on a kilometer-long cable and its contents released into the upper atmosphere. There, the space junk would harmlessly burn up just like a meteor (流星)  does. Meanwhile, her satellite would roll the container back up so that it could collect more trash.

1.What is focused on in the first paragraph?

A. The types of satellites being categorized into.

B. The tracks of satellites orbiting above the planet.

C. The sources of space junk coming from.

D. The danger that satellites face in space.

2.Why can small pieces of space junk threaten satellites?

A. They travel at a very high speed.

B. They are difficult to track by satellites.

C. They can blow up into millions of pieces.

D. They are as soft as a ball in the air.

3.The underlined words "the errant object" refer to_____.

A. the radar system that scans space junk

B. the space junk that travels in disorder

C. the satellite that doesn't keep its track

D. the camera that can't keep space junk on target

4.According to the Dana's design, space junk in her satellite___________.

A. will be swallowed and stored in its trash bin

B. will be broken apart in the trash container

C. will be destroyed by heat in the upper atmosphere

D. will be transported to the earth through a cable