The sketch graph shows how the gravitational potential V of a planet varies with distance r from the centre of the planet of radius R₀.

The magnitude of the gravitational field strength at the point r=R equals the

A. area between the graph and the r-axis between r=R and r=R₀.

B. gradient of the graph at r=R.

C. inverse of the gradient of the graph at r=R.

D. value of V at r=R divided by R².

B