Which of the Following Would Best Benefit the Development of Niche

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

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