单项选择题
A.to revolve
B.revolved
C.revolving
D.to be revolved
单项选择题 The piston moves up and down, thus causing the rotational movement of the（）
单项选择题 The piston cooling system may employ similar components, except that a drain tank is used instead of a head tank That means this system （）.
单项选择题 The piston cooling system may employ similar components, except that （） is used instead of a head tank.