A.open;short;after B.closed;short;after C.open;long;before D.closed;long;before
A.Inefficient scavenging;twice B.Inefficient scavenging;1~8 times C.Fewer strokes in a circle;twice D.Fewer strokes in a circle;1~8 times
A.the piston is just coming upward from the bottom dead center B.the piston has moved about one-fifth of the way up C.the piston has moved most of the way up and almost reached the TDC D.the piston has just past the TDC