2. As shown in Figure 1, given that the area of quadrilateral $A B C D$ inscribed in $\odot O$ is 1, and $A C \perp B D$. Then the area of quadrilateral $O A B C$ is ( ).
(A) 0.3
(B) 0.4
(C) 0.5
(D) 0.6
2. C.

Draw $O E \perp B D$ through point $O$ at point $E$.
Then $B E=D E=\frac{1}{2} B D$.
Thus $S_{\text {V抓边OABC }}=\frac{1}{2} A C \cdot B E=\frac{1}{4} A C \cdot B D$ $=\frac{1}{2} S_{\text {田迈㻆 } A B C D}=0.5$.