患龋率最低的是（）
A.上颌前磨牙
B.上颌磨牙
C.上颌前牙
D.下颌前磨牙
E.下颌前牙
参考答案：E
政治文化的基本结构层次？
Two well-developed high pressure areas may be separated by a（）.
A.Hill of low pressure
B.Trough of low pressure
C.Valley of low pressure
D.Ridge of low pressure
