问题 请问这句话中的is可不可以改will be

The next train is from here to London in six hours' time. 按照时态in six hours' time，请问各位老师把is可以改成will be吗？如果不可以的话，请讲解一下。谢谢！

问题 句式分析：The dish is served cold.

The dish is served cold.请问：该句是主系表结构吗？served是什么成分？

话题 what the matter is

话题 it is no good

话题 it is time that...

话题 So this is it

话题 which is to say

话题 which I belive is

话题 it is fun doing

话题 than is the case

话题 All you do is

话题 What he does is

话题 What he enjoys is...

话题 which it is expected

话题 as is well known