Avalley breeze is created when
a. valley air heats up during the day and rises up the side of the mountain.
b. mountain air cools down at night and sinks down the side of the mountain.
c. valley air cools down at night and rises up the side of the mountain.
d. mountain air heats up during the day and sinks down the side of the mountain.

The answer is A. VALLEY AIR HEATS UP DURING THE DAY AND RISES UP THE SIDE OF THE MOUNTAIN

Explanation: Valley breeze is the breeze that blows up valleys on clear days. It is produced during the day when the floor of a valley is rapidly warm by the sun and causes the warm air to expand and rises up the slopes of surrounding mountains and hills through convection to create a valley breeze.

During the night the slopes get cooled and the dense air lowers into the valley as the mountain wind.