Garth’s distributing contracted with wally co. to sell it bottled water for $20,000. the contract is silent about assignments. garth’s owed $18,000 to zeta corp., so after garth’s delivered the bottled water to wally, garth’s assigned to zeta all of its rights to receive money under the bottled water contract with wally. zeta informed wally of the assignment and demanded that wally make the payment. if wally refuses to pay zeta and zeta sues wally,

a. wally prevails because it did not give permission for the assignment
b. wally prevails because the assignment is for an amount more than the amount that garth owed wally so is against public policy
c. zeta prevails because assignments like this are generally valid
d. zeta prevails, but only if the assignment is signed and in writing