The straight line (x/a)+(y/b)=1 cuts the coordinate axes at A and B . Find the equation of the circle passing through O(0,0), A and B .
A. x²+y²−ax−by=0
B. x²+y²−2ax−2by=0
C. x²+y²+ax+by=0
D. x²+y²=a²+b²