—Did you look up the time of trains to Shanghai?—Yes the earliest train is to leave at 5:

问题补充：

—Did you look up the time of trains to Shanghai?

—Yes, the earliest train is to leave at 5:30 am.

A. likely

B. about

C. possible

D. due

答案：

A. likely

B. about

C. possible

(答案→)D. due

解析：选D。be due to do意为“应该…/预期的”；be about to do 不和时间状语连用；possible主语应为it；而likely与句意不合。