溶血性贫血

A．贫血和出血程度一致
B．贫血和出血程度不一致
C．有贫血而无出血
D．有出血而无贫血
E．无出血亦无贫血

David knocked at the door for nearly half an hour______Mary opened it, unwilling.

A．when

B．while

C．until

D．before