心脏内以及心脏和动脉之间的瓣膜使血液的流动只能是( )
A:右心房→右心室→肺动脉
B:左心室→左心房→主动脉
C:肺动脉→右心房→右心室
D:主动脉→左心房→左心室
I don't think sixteen-year-olds should _____to go to an Internet cafe.
下列大洲被本初子午线穿过的是( )