If $$\sec^{2} \theta + \tan^{2} \theta =3\frac{1}{2}, 0^{\circ} < \theta < 90^{2}$$, then $$\left(\cos \theta+ \sin \theta \right)$$ is equal to

A

$$\frac{1+\sqrt{5}}{3}$$

B

$$\frac{2+\sqrt{5}}{3}$$

C

$$\frac{1+\sqrt{5}}{6}$$

D

$$\frac{9+2\sqrt{5}}{6}$$