Alex Buys a Picture for £50,000 from Betty, a Dealer

Alex buys a picture for £50,000 from Betty, a dealer, who sells it as the work of Constable, a famous painter. Had the picture been genuine, as Betty had promised, it would have been worth at least £70,000. In fact, it is a work by a lesser-known disciple of Constable worth only £1,000. If Alex retains the picture, what is his expectation interest?

A) £69,000.
B) £50,000.
C) £49,000.
D) £20,000.