Air masses are large air volume at constant humidity and a temperature it moves by convection in the atmosphere. The direction is from west to east.
Directions are the path or the points of something or an object. The earth has four major directions one towards the upper side called north, downwards called south, towards the left known as the west, and towards the right called east.
The image shows the movements of the arrow from the left to the right side. On the left is, the west and towards the right is the east.
Therefore, option a. from west to east is the movement of the air masses.
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