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 if Guardian Security pays.
B) ​an illusory contract.
C) ​barred by the preexisting duty rule.
D) ​barred by the doctrine of promissory estoppel.