Speed, Velocity or Acceleration? The subway car begins to
slow down as it makes its
way to the train station.

Acceleration

Explanation:

Speed is how fast something moves.

Velocity is how fast it moves and in what direction it moves in.

Acceleration is the change in how fast it moves. I.e. if it speed up or slows down.

Here we are not given a speed, but are told that the subway car slows down (a negative change in speed), which is a change in speed, therefore it is acceleration (or more accurately deceleration as it is negative acceleration, slowing down, but acceleration is usually used to describe both.)

Hope this helped!