Which of the Following Would Best Benefit the Development of Niche

Which of the following would best benefit the development of niche marketing?

A) a decline in the cost of advertising on radio and newspapers enabling firms to more efficiently reach a wide audience
B) a Supreme Court ruling that limits the market share individual firms in a market are allowed to serve
C) a growing acceptance of free trade agreements such as NAFTA
D) a manufacturing improvement enabling firms to more efficiently design and produce specialized products for small groups of consumers