Rebecca Owes Ian $5,000

Rebecca owes Ian $5,000.Ian needs money in a hurry so he assigns his right to collect from Rebecca to Janet for $4,500.Several days later,Ian assigns his right to collect from Rebecca to Kristin for another $4,500.Ian then leaves town.Kristin is the first to notify Rebecca of the assignment.In the majority of states,which of the following best describes this situation?

A) Rebecca need pay only Janet,since Janet was the first to receive the assignment.
B) Rebecca need pay only Kristin,since Kristin was the first to give notice to Rebecca.
C) Rebecca must pay both Janet and Kristin,since a valid assignment was made to each.
D) Rebecca need pay only Ian,since debts are not assignable.