If a circle passing through point $(2,1)$ is tangent to both coordinate axes, then the distance from the center of the circle to the line $2 x - y - 3 = 0$ is
A．$\frac { \sqrt { 5 } } { 5 }$
B．$\frac { 2 \sqrt { 5 } } { 5 }$
C．$\frac { 3 \sqrt { 5 } } { 5 }$
D．$\frac { 4 \sqrt { 5 } } { 5 }$