如图所示，a、b、c、d为某匀强电场中的四个点，且ab∥cd、ab⊥bc，bc=cd=2ab=2L，电场线与四边形所在平面平行．已知φ_a=16V，φ_b=20V，φ_d=4V．一个质子经过b点的速度大小为v₀，方向与bc夹角为45°，一段时间后经过c点，e为质子的电量，不计质子的重力，则（   ）

Jim tried his best to raise his spirits though he failed the exam.      

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“拎”按部首查字法应查____部，再查____画，组词____

— Yes. Our teacher often tells us we can't be _______ careful while taking exams.