The mean proportional of $$\left(a + b\right) \left(a - b\right)^{3}, \left(a + b\right)^{3} \left(a - b\right)$$

A

$$\left(a+b\right)^{2} \left(a-b\right)2$$

B

$$\left(a+b\right)^{2}\left(a-b\right)$$

C

$$\left(a+b\right) \left(a-b\right)2$$

D

$$a^{2}-b^{2}$$