Only when the villagers were faced with water shortage___       how serious the problem of water pollution was．

A．did they realize

B．will they realize

C．they did realize

D．were they realized

输液出现空气栓塞时应立即采取的体位是( )

A．右侧卧位
B．俯卧位
C．左侧卧位
D．头高足底位
E．端坐卧位