Use Figure: Externalities and Deadweight Loss I

Use Figure: Externalities and Deadweight Loss I. The figure shows the marginal private benefit, marginal social benefit, and marginal private cost for a good. The government should offer a _____ subsidy to arrive at the socially optimal quantity.
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Figure: Externalities and Deadweight Loss I

A) $5
B) $10
C) $15
D) $20