After an Accident with a Vehicle Licensed to Guardian Security

Multiple Choice

After an accident with a vehicle licensed to Guardian Security Company,Heidi signs a covenant not to sue Guardian Security for damages in a tort action if it pays for the damage to her car.This covenant is

A) a bar to recovery only if Guardian Security pays.
B) an illusory contract.
C) barred by the preexisting duty rule.
D) barred by the doctrine of promissory estoppel.