Wind speeds increase higher up from the Earth's surface because

Athe atmosphere is composed of heavier molecules at lower atmospheric levels.
Bthe wind is augmented by the solar wind.
Cfriction from landscape features doesn't slow them down.
Doxygen levels are decreased, making air movement quicker.

Verified Answer :

The correct answer for the question that is being presented above is this one: "A. the atmosphere is composed of heavier molecules at lower atmospheric levels." Wind speeds increase higher up from the Earth's surface because the atmosphere is composed of heavier molecules at lower atmospheric levels. 

C. friction from landscape features doesn't slow them down.