Four charges are arranged at the corners of a square as shown in the figure. Q1 is at (-L/2,L/2), Q2 is at (L/2,L/2), point a is at the origin and Q1-Q2=-Q3=-Q4. Which of the following statements correctly describe the electric field E and the potential at points a,b and c? (Give ALL correct answers, i.e., B, AC, BCD...) A) The E field at a is zero. B) The E field at c points towards b. C) The potential at a is greater(more positive) than the potential at c. D) The potential at b is zero. E) The E field at c is perpendicular to the x axis. F) a,b, and c all lie on the same equipotential surface. G) The magnitude of the E field at b is greater than at C.