Barry owned an office building that was substantially damaged by fire. Barry wants to hire Watson to make the necessary repairs and is told by Watson that he (Watson) does not have good credit due to a family illness and would therefore have trouble obtaining credit. Barry and Watson agree upon and include a clause in the construction contract that states that Barry "promises to pay anyone who provides goods and materials to Watson for use in the repair of the building." The contract also provided that the parties' duties were "non-assignable." Watson paid for all of the materials he ordered except for the last $1,000 of lumber. Watson sent a letter to the supplier and told him that he was unable to pay the bill at the present time. He also included a copy of the contract with the letter to advise the supplier, for the first time regarding the terms of his agreement. Watson asked Barry to pay the supplier and Barry refused, citing a business turndown and a severe illness in his own family. Barry told Watson that he was selling the building to Carla and wanted a release from the contract. Watson felt sorry for Barry and sent him a letter releasing him from the contract and agreeing to complete the repairs for Carla. Watson sent a copy of this letter to the supplier. Watson completed the work and then Barry paid the total contract price (but not the $1,000 to the supplier). Watson ran out of money before he paid the supplier. In an action by the supplier against Barry, on the Barry-Watson contract, Barry's best argument in his defense is that: 

 a) The non-assignment clause in Barry-Watson contract is void as against public policy. 

b) The supplier has not materially changed its position in reliance upon the Barry-Watson contract. sa 

c) Third parties cannot acquire valid claims under this type of contract. 

d) Barry relied to his detriment on Watson's letter of release.