The gradients are positive and negative, so the negative gradients are smaller: b and c are negative. The gradient at c is very steep so has a higher magnitude than b so c is the least, followed by b.
The gradient at d=0 so is the least of the other gradients. a is next because it is a little greater than zero being close to a turning-point (like b). Finally, e is the greatest gradient. So the order from least to greatest is: c, b, d, a, e.