问题补充：
---When are you going to travel to Beijing?
---The train at six tomorrow morning, and I for the station at four o’clock.
A. leaves, leaves
B. is going to leave, am going to leave
C. is going to leave, leaves
D. leaves, am going to leave
答案：
A. leaves, leaves
B. is going to leave, am going to leave
C. is going to leave, leaves
(答案→)D. leaves, am going to leave
解析：句意，这是两个人之间的对话。第一个人说：“你什么时候去北京旅游？” 第二个人说： “明天早晨六点的火车，我四点钟出发去车站。” 表示按时间表、计划、规定将要发生的动作，用一般现在时；表示按计划或安排将要发生的动作，用现在进行时，需要注意：此时常与表示将来的时间状语连用，主语往往使人，故选D。
