题目内容：

Technology is changing our lives. Our present aerospace (航天航空)companies are gradually disappearing as private space concerns are being born every day. I'm going to discuss three space­based businesses that are sure to soon influence us all.

First we have to make space travel cheaply and safely. Engine design is the main challenge. To make money in space, the cost of space travel will have to diminish（减少）. This problem will be the most difficult to solve. Liquid fueled rockets are the only way to get out of Earth's orbit. Finding new ways to power the flight to space is also another big challenge.

Finding the key to cheap space travel might be the biggest story of our times. There are a lot of great minds working on this problem. And companies are pouring money into research and development. In the next few years we'll see the first sub­orbital tourist. And not long after that we should really start to see new and exciting things as competition heats up.

Spacecraft design and production will naturally follow rocket technology. All sorts of crafts will be needed for the wide uses they'll be tasked with. Several companies in the United States have already made small, low­cost test vehicles.

Resources in space will provide great mining profits to those who can afford the cost of setting up such a huge operation. Can you imagine finding a huge asteroid(小行星) of pure gold? The benefit to mankind is limitless. Mining on other planets, like Mars, also adds CO2 into the very thin atmosphere. Over time this can lead to the formation of an atmosphere similar to Earth's.

Space is going to offer us untold opportunity and wealth. But this is only going to occur if wealthy investors step forward and fund the first steps forward. It is certain that technology will take us to worlds we could never have imagined.

1.The passage is mainly about ________．

A．the future of space travel

B．the cost of space travel in the future

C．the development of spacecrafts

D．cheap travel in the future

2.What should be done first to make travel in space cheap and safe?

A．A direct route from Earth to other stars should be found.

B．Some new kinds of fuel should be used in the rockets.

C．New material should be used to build the rockets.

D．New rocket engines should be designed.

3.According to the passage mining on other planets might help ________．

A．increase the travel benefits there

B．form the atmosphere like Earth's there

C．bring some new species there

D．create more job opportunities there

4.According to the passage, the space­based businesses are ________．

A．likely            B．imaginary

C．unbelievable      D．valuable