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Of the six outer planets, Mars, commonly called the Red Planet, is the closest to Earth. Mars, 4,200 miles in diameter and 55% of the size of the Earth, is 34,600,000 miles from the Earth, and 141,000,000 miles from the Sun. It takes this planet, along 0with its two moons, Phoboes and Deimos, 1.88 years to circle, the Sun, compared to 365 days from the Earth.
For many years, Mars had been thought of as the planet with the man made canals, supposedly discovered by an Italian astronomer, Schiaparelli, in 1877. With the United States spacecraft Viking I’s landing on ’Mars in 1976, the man-made canal theory was proven to be only a myth.
Viking I, after landing on the soil of Mars, performed many scientific experiments and took numerous pictures. The pictures showed that the red color of the planet is due to the reddish, rocky Martian soil. No biological life was found, though it had been speculated by many
A. Viking I
B. Deimos
C. the Red Planet
D. Martian

[单项选择]
Of the six outer planets, Mars, commonly called the Red Planet, is the closest to Earth. Mars, 4,200 miles in diameter and 55% of the size of the Earth, is 34,600,000 miles from the Earth, and 141,000,000 miles from the Sun. It takes this planet, along 0with its two moons, Phoboes and Deimos, 1.88 years to circle, the Sun, compared to 365 days from the Earth.
For many years, Mars had been thought of as the planet with the man made canals, supposedly discovered by an Italian astronomer, Schiaparelli, in 1877. With the United States spacecraft Viking I’s landing on ’Mars in 1976, the man-made canal theory was proven to be only a myth.
Viking I, after landing on the soil of Mars, performed many scientific experiments and took numerous pictures. The pictures showed that the red color of the planet is due to the reddish, rocky Martian soil. No biological life was found, though it had been speculated by many
A. Mars is larger than the Earth.
B. Mars had Viking as its moon.
C. Martian soil is brownish rod.
D. It takes longer for Mars to circle the Sun than it takes the Earth.

[单项选择]Someday, in 62 the outer planets of our solar system, humankind will want to do 63 send small probes that merely fly rapidly by them. In time, we will want 64 spacecraft that will go 65 orbit around these alien planets, land robots on their moons, and even return rock and soil sample back to Earth. 66 , we will want to send humans to their moons, on at least 67 which liquid water—the fundamental requirementfor life 68 we know it—is believed to be 69 .
For missions such as these, we will need rockets powered by a nuclear reaction 70 igniting chemicals. Chemical rockets have served us well. But the 71 low amount of energy that they can deliver for a given mass of fuel is a severe 72 when dispatching spacecraft 73 long distances. To reach the outer planets, for example, a chemically-powered space vehicle must 74 fuel by having a very small mass
A. at
B. on
C. into
D. along