Use the Following Figure to Answer the Question : Figure

Multiple Choice

Use the following figure to answer the question : Figure 20-1 : D₁ and S₁ are the private demand and supply curves,of a commodity produced by a competitive firm.S₂ reflects the social marginal cost of production,while S₀ represents the external marginal cost.
-From Figure 20-1,we can infer that the efficient output is:

A) 900 units.
B) 500 units.
C) 400 units.
D) 600 units.