Mary Agrees to Sew Georgia's Prom Dress for $50 Plus

Mary agrees to sew Georgia's prom dress for $50 plus costs. Georgia decides that she wants ruffles around the neck and calls Mary who says it will now cost $60. When Mary finishes the dress (with ruffles) , Georgia must pay:

A) $50, since that is the original agreement.
B) $50, since a modification must be in writing.
C) $60, since the modified agreement is supported by additional consideration.
D) $60, since any subsequent agreement is enforceable.