Four Particles, Each with Mass M, Are Arranged Symmetrically About $\uparrow$

Four particles, each with mass m, are arranged symmetrically about the origin on the x axis. A fifth particle, with mass M, is on the y axis. The direction of the gravitational force on M is:

A) $\uparrow$
B) $\downarrow$
C) $\leftarrow$
D) $\rightarrow$
E) none of these directions