Right answer is (a) Fa+Fp+Fg=Fl
The explanation is: The correct equation is Fa+Fp+Fg=Ft where Fa=aerodynamic forces, Fp=propulsive forces, Fg=gravitational forces and Fl=inertial forces. The statement says that the system of forces containing gravitational forces, aerodynamic forces and propulsive forces results in the inertial forces acting on the aircraft.