Apassenger walks toward the rear of a moving train. describe her motion as seen from a reference point on the train. then describe it from a reference point on the ground.

If the train is moving from Point A to Point B, and this motion we arbitrarily deem "forward", then from the reference point of the train, she will be moving backward. From an external reference point, she will be moving in the same direction as the train, but with a lessened velocity.

Hydrogen is the most abundant element on the periodic table..hope it .

And a) oxygen i believe