引起食品腐败的主要原因是______。
A．水分 B．微生物C．紫外线 D．氧
参考答案：B
Dorothy was always speaking highly of her role in the play, ____, of course, made the others unhappy.
A．who
B．which
C．this
D．what
绿化带应具有（）功能。
A.防噪
B.防尘
C.水土保持
D.改善生态环境功能
