An airplane is flying due east. Earth’s magnetic field has a downward vertical component and a horizontal component due north. Which point on the plane’s exterior accumulates positive charge due to the motional emf?

(a) The nose (the point farthest east)
(b) The tail (the point farthest west)
(c) The tip of the left wing (the point farthest north)
(d) The tip of the right wing (the point farthest south)