大学英语：We are seated in one of the trains

　　1. We are seated in one of the trains， and with us we have a special speedometer that measures their relative speed.

　　2. Furthermore，regardless of which explanation we choose，the end result will be the same.

　　3. Motion(n.行动)-motionless(静止的)

　　4. At the train station we cannot tell whether it was our train or not.

　　5. Only after the other train pulled out of the station could we see that it，and not our train，was moving.本句话为倒装句，由only+状语从句构成+助动词+主语+动词的适当形式+其他