Chords $A B$ and $C D$ of a circle intersect at right angle at the point $P$. If the lengths of $A P , P B , C P , P D$ are $2,6,3,4$ units respectively, then the radius of the circle is:\\
(A) 4\\
(B) $\frac { \sqrt { 65 } } { 2 }$\\
(C) $\frac { \sqrt { 66 } } { 2 }$\\
(D) $\frac { \sqrt { 67 } } { 2 }$