19. 剪床之上刀刃經常傾斜安裝，其目的是 (A)製造容易 (B)安裝拆卸方便 (C)省力易於剪切 (D)美觀

3.A block of mass 1 kg rests on a horizontal table for which the coefficient of static friction is 0.75.One can apply a force to pull the block. Let's say the force makes an angle of to the horizontal table. What is the minimum value of the force needed to start the block moving? (A) 4.56 N(B) 5.88 N (C) 6.92 N (D) 7.35 N (E) 9.02 N.