Which of the following contains a vague pronoun reference?

 - Bella had witnessed a crime, so she made a call to report it. They promptly dispatched police to investigate the scene.
 - Bella had witnessed a crime, so she made a call to report it. The operator promptly dispatched police to investigate the scene.
The second answer choice contains a vague pronoun reference. The pronoun they is used without its antecedent.
The first answer choice shows a possible correction for the vague pronoun reference. They has been replaced with the operator.
Bella had witnessed a crime, so she made a call to report it. The operator promptly dispatched police to investigate the scene.