We know that about seventy percent _____ the earth _____ covered by water.

A．/; is

B．of; are

C．of; is

D．about; are

穿刺颌下区最可能抽出的液体()

A．黄色黏稠脓液

B．暗灰色稀薄脓液

C．陈旧性血性液体

D．黄色蛋清样液体

E．淡黄色清亮液体