He ____ in our school for 20 years and he ____ here in 1977. [ ]

A. has taught; came

B. has taught; has come

C. taught; came

D. has taught ; has came

如图所示，让小球从A点静止释放，运动到C点时，若一切外力全部消失，则小球会沿______

路线继续运动，你判断的依据是______________________________________。