d means the error, but that's quite the same as what you said...
and neither A nor B is correct. imagine the case that you want to divide a by 1000.
(1) c = a * b, where b = 0.001, then
dc / c = db / b = 1
(2) c = a / b, where b = 1000, then
dc / c = db / b = 0.0000001

now compare this with the sample from above. there the multiplication was better. here your multiplication leads to an uncertainty of 100% (!).

the general formula to calculate the error propagation is