钻石成型阶段主要采用（）实施加工。
A.细磨工艺
B.粗磨工艺
C.车钻工艺
D.A+B+C
参考答案：D
A．It costs much more than its worth.
B．It should be brought up-to-date.
C．It calls for immediate repairs.
D．It can still be used for a long time.
如图所示，质量为m的木块，被水平力F紧压在倾角为θ=60°的固定木板上静止，木板对木块的作用力（压力与摩擦力的合力）为：
