If x=rsinAcosB,y=rsinASinB and z= r cosA find the value of $$x^{2}+y^{2}+z^{2}$$

A

$$2r^{2}$$

B

$$\frac{3}{2} r^{2}$$

C

$$r^{2}(cos^{2}B+cos^{2}A)$$

D

$$r^{2}$$