问题
选择题
He was wearing dark glasses to _____ his eyes from the sun. [ ]
A. stop
B. keep
C. prevent
D. protect
答案
答案：D
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He was wearing dark glasses to _____ his eyes from the sun. [ ]
A. stop
B. keep
C. prevent
D. protect
答案：D
,物体B重
,A与B、B与地的动摩擦因数相同｡用水平绳将物体A系在竖直墙壁上,水平力F向右拉物体B,当
时,才能将B匀速拉出｡求接触面间的动摩擦因数多大?