any ideas?

The figure here shows four situations in which charged particles are at equal distances
from the origin. Rank the situations according to the magnitude of the net electric
field at the origin, greatest first.
http://img442.imageshack.us/img442/876/cp2302sw3.th.jpg (http://img442.imageshack.us/my.php?image=cp2302sw3.jpg)

i'm writing an online self quiz and i'm too lazy to look up the answer, i've got about 30 minutes left and it's the last question. any ideas? if i don't get a response i'm just going to go wih my best guess and retake it later.

c - d- b - a :dunno: I'd pick if I had to, but I have no idea.

that's what i was thinking.

finished the test, 100%. easiest quiz i've had in university lol.
i guess this thread is now useless, it can be deleted or locked or whatever

oops nevermind, i didn't read it correctly, it was wrong. they all have the same magnitude