全身骨骼中变化最为显著的为（）
A.牙冠
B.牙根
C.牙颈
D.牙周膜
E.牙槽骨
参考答案：E
解析：牙槽骨基本依赖包裹它的牙龈组织来供养。
A series of debates between the major candidates ________ scheduled last week.[ ]
A. is
B. are
C. was
D. were
吸收塔运行中液位维持在（）mm。
