Answer :
While the shop owner was reviewing his purchases, he realized that his inventory of various items tended to fluctuate with the time of year. For example, he sold much more eggnog in the winter and almost none in the summer.
The amount of turkeys sold fluctuated during the months of November and December, which cause the meat department manager to keep an updated inventory of the birds.
Inventory as a noun refers to how much you have of something. Inventory as a verb is the action of counting how much you have of something. A synonym of fluctuate is change. Usually with fluctuate there's a sense that things are constantly changing back and forth.
