After Landing on an Unexplored Klingon Planet, Spock Tests for the Direction

After landing on an unexplored Klingon planet, Spock tests for the direction of the magnetic field by firing a beam of electrons in various directions and by observing the following:
Electrons moving upward feel a magnetic force in the NW direction;
Electrons moving horizontally North are pushed down;
Electrons moving horizontally South-East are pushed upward.
He naturally concludes that the magnetic field at this landing site is in which direction?

A) E
B) NE
C) SW
D) SE
E) W