Having mastered the technology of manned spacecraft, China became the third country in the

world ______ manned spaceflight independently.[      ]

A. to develop    

B. developing    

C. developed    

D. develop

汽车在十字路口处沿图中虚线由西向北转弯，从A到B段曲线为圆弧。视汽车车厢为刚体，在A至B这段路程中，该刚体作（）

A.圆周运动

B.曲线运动

C.曲线平动

D.定轴转动