Abusinesswoman entered into a written contract with a general contractor to build a studio and broadcast transmitter for $3 million by july 1. among his tasks, the contractor was to install underground cables and fiberoptic lines necessary to broadcast. when digging the deep trench necessary to lay the conduit containing the fiberoptic lines, the contractor encountered a stretch of extremely soggy soil. this was an indication that an offshoot of the nearby city's aquifer underlay the property. this was not indicated on any of the geological survey maps available in the office of the county recorder of deeds. the contractor told the businesswoman that it would cost an additional $50,000 to lay the conduit through that stretch of soil. the businesswoman had already launched an advertising campaign indicating that the station would begin broadcasting on july 4, which was rapidly approaching. therefore, when the contractor threatened to quit the job without the additional $50,000, the businesswoman reluctantly agreed orally to the contractor's demand as long as he promised that all of the work would be completed by the middle of june. the contractor agreed, proceeded to lay the conduit, and completed building the studio and transmitter by june 15. the businesswoman paid the contractor $3 million, but when the contractor demanded $50,000 more, she refused to pay it. the contractor sues the businesswoman for the $50,000.who will prevail? a the businesswoman, because the oral modification was not effective to alter the prior written agreement. b the businesswoman, because no valid consideration was provided for the agreement to pay the additional $50,000.c the contractor, because the modification was supported by consideration. d the contractor, because he detrimentally relied on the businesswoman's promise to pay the additional $50,000.