--What are your school ________, Jack?

-- Well, at school we have to wear school uniforms.

A．subjects

B．uniforms

C．classes

D．rules

斜轴式轴向柱塞泵改变排油方向是靠改变（）。

A．转向

B．缸体偏摆方向

C．斜盘倾斜方向

D．浮动环偏心方向