C

Step 1: The car accelerates at \(5\, m/s^2\) for a time \(t = 4\, s\). Thus, the velocity of the car at \(t = 4\, s\) is given by the formula:
\[ v = u + at = 0 + (5)(4) = 20\, m/s \]
Step 2: When the ball is dropped from the window, it has the same velocity as the car at that moment, which is \(20\, m/s\) in the horizontal direction. The ball also starts to fall under gravity. The vertical acceleration of the ball is due to gravity, which is \(g = 10\, m/s^2\). The ball has a horizontal velocity of \(20\, m/s\) and a vertical acceleration of \(10\, m/s^2\).
Therefore, the answer is \(20\, m/s\) for horizontal velocity and \(10\, m/s^2\) for vertical acceleration.