唯一有关的，就是点a和点b的，高度差。
The only thing that matters is the difference in height between point a and point b.
这是给定的条件-，点a点b之间，存在高度差。
It's a given — there is a height difference between a and between b.
注意站台与列车之间的高度差及空隙。
Please mind the gap and height difference between the train and platform.
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