The angles of a quadrilateral are in arithmetic progression, and the greatest angle is double the least. Find the angles of the quadrilateral in radians:
a) π/6, π/3, π/2, π
b) π/4, π/2, 3π/4, π
c) π/6, π/4, π/3, π/2
d) π/2, π, 3π/2, 2π