Answer:
d. Every second, the truck’s velocity increases by 3 km/h to the south.
Explanation:
Acelleration can be defined as change of velocity over change of time.
That's why if we say: "A truck accelerates 3 km/h/s south."
We are saying that the acceleration of the truck variate 3Km/h wich is velocity of the truck, and it variates every second and also its direction is south.