Mars is the _____ planet from the Sun.

The passage is mainly concerned with ______.

A．the feasibility of life existing on other planets

B．the description of Mars's physical environment

C．the comparison between the physical features of Mars and the Earth

D．the feasibility of men's migrating onto Mars

A.The Possibility of Life on the Mars

B.Future Conditions on the Mars

C.The Mars and the Earth

D.A Study of the Climate of the Mars

A．Scientists from "Mars Underground" want to stay on Mars for a lifetime.

B．Scientists from "Mars Underground" have been paying attention to the manned missions that we have been sending to Mars.

C．Even if there is any life on Mars, it is not an intelligent one.

D．We will send astronauts to Mars within ten years.

A.Earth's moon used to orbit Mars.

B.Mars was captured by the gravitational field of the Sun,

C.A planet the size of Mars collided with Earth.

D.Mars is larger than Earth.

The author of this passage is mainly concerned with______.

A．the significance of discovery of water on the Mars

B．the achievements of U.S. in exploring the Mars

C．the performance of five craft launched to Mars

D．the fate of the science of Mars exploration

According to the passage, what has been a major focus of research about Mars？

A．How Mars compares to other planets in the solar system

B．Who built the network of canals on the surface of Mars

C．Whether signs of water indicate that life has existed on Mars

D．How soon astronauts from Earth will be able to go to Mars

A．copying

B．mocking

C．simulating

D．pretending