Ingrid Has Been Waiting for the Show "Mamma Mia!" to Come

Ingrid has been waiting for the show "Mamma Mia!" to come to town.When it finally does come,ticket prices are $60.Ingrid's reservation price is $75.But when Ingrid tries to buy a ticket,they are sold out.
Refer to the information above.Sven had purchased a ticket at the ticket window for $60.Sven's reservation price is $65.If Sven attends "Mamma Mia!" and Ingrid does not,it is:

A) inefficient because Sven and Ingrid could have made a mutually beneficial trade.
B) efficient because Sven paid less for the ticket than his reservation price.
C) efficient because Sven arrived at the ticket counter before the show was sold out.
D) inefficient because ticket prices are regulated by the government.