透明玻片上的“9>6”，用显微镜观察到的是 [ ]
A．9>6
B．6<9
C．6>9
D．9<6
答案：D
Do you know ________
A．what is this used for
B．what this is used for
C．which this is used
D．that this is used for
齿数与啮合圆（节圆）直径之比称为齿轮模数。
