Inside an aeroplane, flying at high altitude,
(A) The pressure is the same as that of outside
(B) Normal atmospheric pressure is maintained by the use if air pumps
(C) The pressure inside is less than the pressure outside
(D) Normal humidity and partial vacuum are maintained

Hint: Atmospheric pressure reduces with increasing height. The human body cannot survive at low pressures. A body open to the atmosphere has a pressure equal to the pressure of the immediate atmosphere surrounding it. So inside the aeroplane, normal pressure is maintained where the human body can survive.

Complete step by step solution:
In general, the atmospheric pressure is the force exerted by the atmosphere on a unit surface area. The atmospheric pressure at a level is a result of the weight of the atmospheric air above that point exerted on the molecules within a unit surface area at the level. Now, this means that when we are at the lowest level of the atmosphere the pressure is highest since the pressure there is as a result of the weight of the entire atmosphere above it. Thus, as we move higher up the atmosphere the pressure must reduce, since the weight of the atmospheric air above it has reduced. This is because some of the atmospheric air is now below the said level. Hence, at high altitudes the atmospheric pressure around the plane must be low.
However, humans have been known to be terrestrial beings i.e. live and thrive at the surface of the earth, hence cannot survive at lower pressures or higher pressures than surface pressure. This implies that an airplane, cruising at high altitudes which has low pressure, must somehow maintain the normal pressure humans are used to.
Thus, we can conclude that normal atmospheric pressure must be maintained by the use of air pumps.
Hence, the correct option is B.

Note:
Another possible way to maintain pressure within a body at high attitudes will be to seal it air tight before taking it to a lower pressure location. When the container is sealed the higher pressure air inside is isolated from the lower pressure outside and thus will not interact, hence maintaining its higher pressure. However, this is unrealistic for an airplane which of course contains people who have to breathe.