GP Had Been Contracted by the City of Kingston to Install

GP had been contracted by the city of Kingston to install a monitoring system at all public places.This was to be done in two phases and the city had the right to terminate the contract.GP had plans to use a subcontractor,Rex,whom they usually hired for the last phases of projects executed by them.After two weeks of the work,the city of Kingston found that things were not going properly and terminated GP's contract.Can Rex sue the city of Kingston?

A) Yes,because Rex is a third-party donee beneficiary.
B) No,because Rex is only an incidental beneficiary.
C) Yes,because Rex is involved in a novation.
D) No,because donee beneficiaries cannot enforce a contract.