For some time the expert __________ people of the health risks caused by passive smoking. He     says he won't stop until all the smokers around him decide to quit smoking.

A．is warned

B．is warning

C．has been warning

D．has been warned

汉代的衡量单位为铢，几铢等于一两（）

A.24

B.25

C.12

D.16

E.20