Answer: C. Acceleration
Explanation:
Acceleration [tex]a[/tex] is defined as the variation of Velocity [tex]\Delta V[/tex] in time [tex]\Delta t[/tex] :
[tex]a=\frac{\Delta V}{\Delta t}[/tex]
In addition, acceleration is a vector quantity (like velocity) and as a vctor it has magnitude and direction. When one of this aspects changes (or both) acceleration changes as well.
So, if the car keeps the same speed ([tex]40 km/h[/tex]) but changes its direction, its acceleration changes.