The correct answer is C. else.
The sentence “Make haste else we shall miss the train” means that we need to hurry or else we will miss the train. The word “else” is used to introduce a consequence or alternative. In this case, the consequence of not hurrying is that we will miss the train.
The other options are not correct because they do not make sense in the context of the sentence. The word “either” is used to introduce two or more options, but there is only one option in this sentence: we need to hurry. The word “or” is also used to introduce two or more options, but it does not have the same meaning as “else”. The word “neither” is used to introduce two or more negative options, but there is no negative option in this sentence.
In conclusion, the correct answer is C. else.