1. The weight of an aeroplane flying in the air is balanced by

(a)      Vertical component of the thrust created by air currents striking the lower surface of the wings

(b)  Force due to reaction of gases ejected by the revolving propeller

(c)   Upthrust of the air which will be equal to the weight of the air having the same volume as the plane

(d)  Force due to the pressure difference between the upper and lower surfaces of the wings created by different air speeds on the surfaces

Ans. d