In the Last 15 Years, Mobile Phone Prices Have Been

In the last 15 years, mobile phone prices have been dropping significantly while the technology and features offered in these phones has increased dramatically. Along with technology advancement and outsourcing the production of mobile phones to countries with low cost of labor such as China, which of these economic phenomena explains the reduction in price?

A) The substitution effect.
B) Competition.
C) The income effect.
D) Elasticity of Demand.