问题
单项选择题
教室前排桌距黑板不应少于（）。
A.3.0m
B.2.5m
C.2.0m
D.1.5m
E.1.0m
答案
参考答案：C
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教室前排桌距黑板不应少于（）。
A.3.0m
B.2.5m
C.2.0m
D.1.5m
E.1.0m
参考答案：C
It was July 1976. An unmanned spaceship, Viking One, had arrived at Mars. On July 20th, the spaceship . Part of it continued toward a landing on the planet. It fell through the late afternoon Mars’ sky. Forty kilometers above the planet, the thin began to slow its fall. Six kilometers above the planet a big parachute(降落伞)opened. The landing craft fell more slowly. Then, three rocket engines . And the landing craft set down on the surface. in the Viking One Lander immediately sent a message to the earth. It said, “I am here. I am down safely. I am beginning my work. ” The message at the speed of light. It took twenty minutes to reach the earth, more than three hundred and twenty million kilometers . Scientists and engineers at the control center . Moments later, television receiver in the control center began to the first picture from Viking One. People at the center could see the feet of the landing craft sitting firmly on the 11 soil of Mars. Those pictures were our first look at the planet. They showed a red surface, full of rocks, with no sign of . It was our first look at a planet that is full of surprises, mysteries and promise. Viking One was launched toward Mars in August, 1975. The spaceship had two : an orbiter(轨道飞行器)and a lander(着陆器). The orbiter would circle Mars. It would take pictures of Mars’ surface. It would the atmosphere. The would go down to the surface. It would carry to dig up and study soil and . It also would report about any evidence of life on the planet. The lander would send this to the orbiter and then back to the earth.
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