Anna contracts with Andrew's Roofing Co. to roof her house for $3,000. The roofer finishes and she pays him. The next week, in a mild windstorm with winds not exceeding 10 MPH, all of the shingles blow off. Andrew's Roofing Co. says he will fix the roof for an additional $2,000. Anna agrees

a.) Anna is stuck because this was an unforeseen difficulty

b.) Anna need not pay because her first payment was past consideration

c.) Anna need not pay because roofer was under a pre-existing duty to roof the house in a reasonable manner

d.) none of the above