Two variable chords AB and BC of a circle `x^(2)+y^(2)=a^(2)` are such that `AB=BC=a`. M and N are the midpoints of AB and BC, respectively, such that the line joining MN intersects the circles at P and Q, where P is closer to AB and O is the center of the circle.
The locus of the points of intersection of tangents at A and C is
A. `60^(@)`
B. `90^(@)`
C. `120^(@)`
D. `150^(@)`
