题目内容：

    “Two centuries ago, Lewis and Clark left St. Louis to explore the new lands acquired in the Louisiana Purchase,” George W. Bush said, announcing his desire for a program to send men and women to Mars. They made that journey in the spirit of discovery. America has ventured forth into space for the same reasons.”

Yet there are vital differences between Lewis and Clark’s expedition and a Mars mission. First, they were headed to a place where hundreds of thousands of people were already living. Second, they were certain to discover places and things of immediate value to the new nation. Third, their venture cost next to nothing by today’s standards. A Mars mission may be the single most expensive non-wartime undertaking in U.S. history.

Appealing as the thought of travel to Mars is, it does not mean the journey makes sense, even considering the human calling to explore. And Mars as a destination for people makes absolutely no sense with current technology.

Present systems for getting from Earth’s surface to low-Earth orbit are so fantastically expensive that merely launching the 1,000 tons or so of spacecraft and equipment a Mars mission would require could be accomplished only by cutting health-care benefits, education spending, or other important programs—or by raising taxes. Absent some remarkable discovery, astronauts, geologists, and biologists once on Mars could do little more than analyze rocks and feel awestruck(敬畏的) staring into the sky of another world. Yet rocks can be analyzed by automated probes without risk to human life, and at a tiny fraction of the cost of sending people.

It is interesting to note that when President Bush unveiled his proposal, he listed these recent major achievements of space exploration pictures of evidence of water on Mars, discovery of more than 100 planets outside our solar system, and study of the soil of Mars. All these accomplishments came from automated probes or automated space telescopes. Bush’s proposal, which calls for reprogramming some of NASA’s present budget into the Mars effort, might actually lead to a reduction in such unmanned science—the one aspect of space exploration that’s working really well.

Rather than spend hundreds of billions of dollars to hurl tons toward Mars using current technology, why not take a decade or two or however much time is required researching new launch systems and advanced propulsion (推进力)? lf new launch systems could put weight into orbit affordably, and advanced propulsion could speed up that long, slow transit to Mars, the dream of stepping onto the red planet might become reality. Mars will still be there when the technology is ready.

1.What do Lewis and Clark’s expedition and a Mars mission have in common?

A.Instant value.

B.Human inhabitance.

C.Venture cost.

D.Exploring spirit.

2.Bush’s proposal is challenged for the following reasons except that     .

A.its expenditure is too huge for the government to afford.

B.American people’s well-being will suffer a lot if it is implemented

C.great achievements have already been made in Mars exploration in America

D.unmanned Mars exploration sounds more practical and economical for the moment

3.Which cannot be concluded from the passage?

A.Going to Mars using current technology is quite unrealistic.

B.A Mars mission will in turn promote the development of unmanned program.

C.Bush’s proposal is based on three recent great achievements of space exploration

D.The achievements in space exploration show how well unmanned science has developed.

4.What is the main idea of the passage?

A.Risky as it is, a Mars mission helps to retain Americas position as a technological leader.

B.A Mars mission is so costly that it may lead to an economic disaster in America.

C.Someday people may go to Mars but not until it makes technological sense.

D.A Mars mission is unnecessary since the scientists once there won’t make great discoveries.