In a Competitive Market,the Market Demand Curve Measures the ________

In a competitive market,the market demand curve measures the ________ if ________ exist. In a competitive market,the market supply curve measures the ________ if ________ exist.

A) marginal social benefit;no external costs;marginal social cost;no external benefits
B) firms' marginal benefit;external benefits;consumers' marginal cost;external costs
C) marginal social benefit;no external benefits;marginal social cost;no external costs
D) marginal social benefit;external benefits;marginal social cost;external costs
E) consumer surplus;external benefits;producer surplus;external costs