Let a,b ` in ` R and `a^(2) + b^(2) ne 0` . Suppose `S = { z in C: z = (1)/(a+ ibt),t in R, t ne 0}`, where `i= sqrt(-1)`. If `z = x + iy` and z in S, then (x,y) lies on
A. the circle with radius `(1)/(2a)` and centre `((1)/(2a),0)` for `a gt 0 be ne 0`
B. the circle with radius `-(1)/(2a)` and centre `(-(1)/(2) ,0) a lt 0, b ne 0`
C. the axis for `a ne 0, b =0`
D. the y-axis for `a = 0, bne 0`