Lucy has the utility function u (x, m) = 100x - x^2/2 +m, where x is her consumption of earplugs and m is money left over to spend on other stuff. if she has$10,000 to spend on earplugs and other stuff and if the price of earplugs rises from$40 to $60, then her net consumer's surplus: 

A. falls by 800.

B. falls by 1,000.

C. falls by 1350.

D. increases by 400.