In the two-cycle engine, the piston ACTS as a valve, clearing valve ports in the cylinder wall as it nears BDC.

在二行程发动机中，活塞起到阀门的作用，当活塞接近下止点时，使气缸壁上的进排气口打开。

youdao

Either way this hybrid organisation serves as the focus, the clearing-house, the engine-room of the European Union.

BBC: By Europe Correspondent David Shukman