"Field Work"

Consider the figure at the right. The blue balls are located at (-1,1,0) and (1,-1,0) each carry a charge, Q. The green balls are located at (1,1,0) and (-1,-1,0). They each carry a charge -Q. There are three points marked in red, O is the origin, P1 is (0,0,2) and P2 is (2,0,0). There are no charges at these points.

Which of the following statements is true?

1. The magnitude of the electric field is greatest at the origin.
2. The magnitude of the electric field is greater at point P2 than at the other two points.
3. The magnitude of the electric field is zero at all three points.
4. The magnitude of the electric field is lower at point P1 than it is at the origin.
5. All of the above.
6. None of the above.