患者，女，19岁，未婚。月经提前，量少、色红、质粘绸，伴手足心热，两颤潮红，舌红少苔，脉细数。治疗应首选：（ ）

A．大补元煎

B．丹栀逍遥散

C．清经散

D．保阴煎

E．两地汤

Air pollution is getting more and more serious, so we must take action ________ it is too late.

A．before

B．after

C．until

D．when