问题
选择题
He has got used to _____ early. [ ]
A. getting up
B. get up
C. has gotten up
D. be getting
答案
答案：A
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He has got used to _____ early. [ ]
A. getting up
B. get up
C. has gotten up
D. be getting
答案：A
的小球穿在长
的直杆上并置于实验室中，球与杆间的动摩擦因数为0.5，当杆竖直固定放置时，小球恰好能匀速下滑。保持风力不变，改变固定杆与竖直线的夹角
，将小球从O点静止释放。g取10m/s2，
，
，求：