口腔生态系包括（）
A.宿主与微生物
B.细菌与病毒
C.病毒与真菌
D.支原体与原虫
E.厌氧菌与需氧菌
参考答案：A
There are many people in the park on weekends. It is very _________. [ ]
A. expensive
B. inexpensive
C. crowded
D. uncrowded
什么是断层破碎带？
