铣削刀具齿槽时，齿向要求是指齿槽必须符合图样规定的直齿槽或螺旋齿槽，以及螺旋齿槽的螺旋角和螺旋方向。
参考答案：对
-I'm very tired these days because of studying for physics.
-Why not ________ music? It can make you ________.[ ]
A. listen to; to relax
B. listen to; relax
C. listening to; relax
D. listening to ; to relax
替代品（Substitutes）
