The locus of the mid-points of the chords of the circle of lines radiùs r which subtend an angle `pi/4` at any point on the circumference of the circle is a concentric circle with radius equal to
A. `x^(2)+y^(2)=1`
B. `x^(2)+y^(2)=(27)/(4)`
C. `x^(2)+y6(2)=(9)/(4)`
D. `x^(2)+y^(2)=(3)/(2)`