Wind speeds increase higher up from the earth's surface because
a. oxygen levels are decreased, making air movement quicker.
b. the wind is augmented by the solar wind.
c. the atmosphere is composed of heavier molecules at lower atmospheric levels.
d. friction from landscape features doesn't slow them down.
i know its not c

Option D

Explanation:

When the wind is moving near to the earth surface , its speed reduces due to the presence of surface objects such as mountains, trees, houses, poles, and all other man made objects.

how ever,  when the wind is moving at a higher altitude (much above the surface obstructions) , the disturbance get reduced  thereby reducing the friction and hence  the speed of the wind increase at higher altitude.

Thus, option D is correct