Answer:
near earth's surface.
Explanation:
As a general rule, friction is greatest near earth's surface.
Near the Earth surface the air density is highest among the all the places given in the option. Now, since the density is higher the thickness of air column will be higher as well and hence The friction is greatest near earth's surface.
This the reason why planes and jet are flown well above the earth's surface so as to avoid losses due to friction.
