Excuse me,when is the next train to Beijing due to depart?B

题目

Excuse me,when is the next train to Beijing due to depart?B
A.The train is expensive.B.In 40 minutes.
C.It hasn’t gone yet.D.Before another one.
请高手翻译下这句话,正确答案选B,为什么选B啊,请高手讲解下其中的语法知识,我将感激不尽,
due to depart在这里是什么意思啊?我主要是这个不懂,

答案

duo to除了有“由于”的意思外,还有“预期”的一层意义,"depart"在这里是“启程”的意思.所以这句话的整体意义是：打扰了,请问去北京的下一班火车大概什么时候启程.