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

Multiple Choice

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