Mural, a wallpaper hanger, sent Gennybelle, a general contractor, this telegram: Will do all paperhanging on new Doctors' Building, per owner's specs, for $14,000 if you accept within reasonable time after main contract awarded./s/ Mural Three other competing hangers sent Gennybelle similar bids in the respective amounts of $18,000, $19,000, and $20,000. Gennybelle used Mural's $14,000 figure in preparing and submitting her own sealed bid on Doctors' Building. Before the bids were opened, Mural truthfully advised Gennybelle that the former's telegraphic sub-bid had been based on a $4,000 computational error and was therefore revoked. Shortly thereafter, Gennybelle was awarded the Doctors' Building construction contract and subsequently contracted with another paperhanger for a price of $18,000. Gennybelle now sues Mural to recover $4,000. Which of the following, if proved, would most strengthen Gennybelle's prospect of recovery? 
After Mural's notice of revocation, Gennybelle made a reasonable effort to subcontract with another paperhanger at the lowest possible price.  Gennybelle had been required by the owner to submit a bid bond and could not have withdrawn or amended her bid on the main contract without forfeiting that bond. Mural was negligent in erroneously calculating the amount of his sub-bid. Gennybelle dealt with all of her subcontractors in good faith and without seeking to renegotiate (lower) the prices they had bid.