Which statement best explains acceleration?

Acceleration is the ratio of a change in velocity to the time over which the change happend

Acceleration is just how fast velocity is changing in a certain time. Simply subtract the final velocity from initial velocity, then take that number and divide that by the change in time. If that sounds familiar, it's because it's the same formula you use to find the slope of a line. If you've done calculus, it's finding the secant line, which means you've found the average acceleration using the (change in v) / (change in t). If you need the instantaneous acceleration, you need to take the derivative of your function at a certain time (also calculus.) ignore the last two sentences if you haven't taken calc1