以初速度v0竖直上抛一个物体,不计空气阻力,物体升高到某一高度时,其重力势能恰好是动能的2倍,则此高度为[ ]
A.
B.
C.
D.
答案:A
If you don't know how to spell new words, ____ in the dictionary. [ ]
A. look up them
B. look for them
C. look them up
D. look them for
东风8B型内燃机车差动继电器,当两组制动风机不平衡电流值达()A时动作。