Troll Corporation Sells Dolls for $10

Troll Corporation sells dolls for $10.00 each in a market that is perfectly competitive. Increasing the number of workers from 100 to 101 would cause output to rise from 500 to 550 dolls per day. The marginal revenue product for the 101st worker is

A) $10.00.
B) $500.
C) $5,000.
D) $1,010.