Tom ______to many places of interest since he moved to China with his family.      [ ]

A. traveled  

B. travels  

C. has traveled  

D. will travel

战标是观测位移时供照准用的，可分为固定战标和活动战标两种。其中固定战标的形式为（）种。

A、战牌式固定战标

B、标杆式固定战标

C、插入式固定战标

D、以上三种都是