A company is under pressure of increasing its gross profit. Accounting Department of the company conducts inventory count at the end of the month. Which of the following presents the greatest reason that the accounting department employee intentionally included nonexistent inventory in the count to increase the ending inventory?

a.The company has low inventory turnover

b. The employee has a habit of gambling and is living beyond his means

c. The company uses periodic inventory system

d.The company uses perpetual inventory system

I know the answer is C, but why?? please explain clearly, thanks