有人由于下颌活动用力过猛,使上下颌不能合拢,这是由于( )
A:关节头从关节囊中脱出
B:关节腔内有积液
C:关节头从关节窝中脱出
D:关节软骨发生病变
He spent every Sunday evening the piano in an old people's home.
While the man ____ (run) back home, he saw a dog by the side of the road.
多项式x3-2x2+5x+3与多项式2x2-x3+4+9x的和一定是( )