呈不规则块状，棕褐色或黑绿色，松脆易破碎，有特异臭气，味极苦。此药材是

A．儿茶

B．五倍子

C．芦荟

D．青黛

E．海金沙

You’d better put a cloth over the salad to ______ the flies for the sake of health.

A．keep off

B．keep out

C．help out

D．hold out