问题
选择题
Athens _____ the birthplace of western civilization.[ ]
A. are known as
B. is known as
C. are known for
D. is known for
答案
答案：B
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Athens _____ the birthplace of western civilization.[ ]
A. are known as
B. is known as
C. are known for
D. is known for
答案：B
，轻弹簧下端固定在斜面底端，弹簧处于原长时上端位于B点，开始时物体A到B的距离为L＝1 m，现给A一个沿斜面向下的初速度v0＝2 m/s，使物体A开始沿斜面向下运动，物体A将弹簧压缩到最短后又恰好被弹回到B点，取g＝10 m/s2（不计空气阻力），求：