Slope of a velocity-time graph gives
he following cases of motions, the distance moved and the magnitude of displacement are equal?
$(a)$. If the car is moving on straight road
$(b)$. If the car is moving in circular path
$(c)$. The pendulum is moving to and fro
$(d)$. The earth is revolving around the sun

The slope of the velocity-time graph shows acceleration.

 So, option $(c)$ is correct.