Ah hah ! The two questions on this page are checking to see if you understand what "net force" means.
Remember that "net force" means the result of adding up the strength and direction of a group of separate forces.
Also remember that if the net force is not zero, then the object accelerates in the direction of the net force.
-- Forces 'B' and 'D' both act horizontally on the airplane. Force-'D' tries to pull it forward, and force-'B' tries to pull it backward. The airplane is moving forward faster and faster. This tells us that the net horizontal force on it must point forward. So force-D must be stronger than force-B.
-- Forces 'A' and 'C' both act vertically on the airplane. Force-A tries to pull it up, and force-C tries to pull it down. At the moment of take-off, the airplane lifts off from the ground and rises up and up. This tells us that the net vertical force on it must point up. So force-A must be stronger than force-C.
