具有输血指征需符合以下标准（）

A.急性失血血红蛋白需下降20g／L

B.慢性贫血血红蛋白低于80g／L

C.急性失血血容量减少大于20％

D.慢性失血血容量减少大于20％

E.慢性失血患者感觉头昏明显时

—You look rather tired. _______stop to take a rest？

—All right. But I’ll have to work for a few more minutes.

A．Why not

B．Why don’t

C．What about

D．How about