Gases exert pressure on the walls of the container because the gas molecules _____.

Which of the following statement is true?

$1$. Both A and B are wrong.

$2$. A and B are correct and B is not the correct explanation of A.

$3$. A and B are correct and B is the correct explanation of A.

$4$. A is correct but B is wrong.

A : At high altitude regions the cooking of food becomes difficult.
B : Water boils at a lower temperature when the pressure is low.