The locus of the points of intersection of the lines `x cos theta+y sin theta=a ` and `x sin theta-y cos theta=b`, (`theta=` variable) is :
A. `x^(2)+y^(2)=a^(2)+b^(2)`
B. `x^(2)+y^(2)=a^(2)-b^(2)`
C. `x^(2)+y^(2)=2(a^(2)+b^(2))`
D. None of the above
