If the curves, $$\frac{x^2}{a} + \frac{y^2}{b} = 1$$ and $$\frac{x^2}{c} + \frac{y^2}{d} = 1$$ intersect each other at an angle of 90°, then which of the following relations is TRUE?

A

$$a - c = b + d$$

B

$$a - b = c - d$$

C

$$a + b = c + d$$

D

$$ab = \frac{c+d}{a+b}$$