Many Entrepreneurs Found Great Economic Opportunities in Selling Mobile Phones

Many entrepreneurs found great economic opportunities in selling mobile phones in the 1990s, but as more entrepreneurs enter the mobile market, the fewer economic the opportunities found. In other words, economic opportunities are exhausted because the additional supply of mobile phones forced down prices. What effect did this have on the profit margin of existing sellers of mobile phones?

A) It had no effect on the profit margin.
B) It increased the profit margin.
C) It decreased the profit margin.
D) None of the above.