If you jump vertically while inside a fast-moving train that is slowing down, you land:

a. a bit behind your original position.

b. at your original position.

c. a bit ahead of your original position.

Answer;

B. at your original position.

Explanation.

It the train does not slow down the to the force of gravity you would land far behind the train. Here, it slows down and you already jumped vertically up, you cover some certain distance from the train up in the air and it is also slowing down you will likely come to your original position.