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1最佳选择题 3分

Spaceenthusiastslooktothedaywhenordinarypeopleaswe

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2最佳选择题 3分

Spaceenthusiastslooktothedaywhenordinarypeopleaswe

A. there is no clear destination in space
B. it is too risky and expensive for people to go beyond the orbit
C. the current space propulsion systems can not meet the needs for the long space travel
D. there is not enough energy for spacecraft to gain velocity

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3最佳选择题 3分

Spaceenthusiastslooktothedaywhenordinarypeopleaswe

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4最佳选择题 3分

Spaceenthusiastslooktothedaywhenordinarypeopleaswe

A. When traveling in space, spacecraft take indirect route to avoid gravity from the other planets.
B. Space engineers are now developing space elevators.
C. It will take the current spacecraft several hundred years to travel to other solar systems.
D. Scientists from different countries are working together to develop new space technologies.

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5最佳选择题 3分

Spaceenthusiastslooktothedaywhenordinarypeopleaswe

A. Current rockets are vulnerable and unstable.
B. New propulsion system has been developed.
C. People consider loser beams as a possible solution to developing new propulsion system.
D. At present, nuclear energies can be used in propulsion systems.

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