Frank, with his two sisters , ______London by train which ______at 8:30 tomorrow morning .[      ]

A. is leaving for ; will leave     

B. are leaving for ; leaves

C. is leaving for ; leaves     

D. will leave for ; will leave

有关牙线，叙述正确的有（）

A.无牙周炎患者不适用牙线

B.消除邻接面牙菌斑最好的方法是使用牙线

C.牙线最主要的功能是去除邻面菌斑

D.牙线在固定桥和矫正器处可用弓形绷架

E.牙线须放入龈沟内清洁