Which order requires a person to stop or start a specific action?

The correct choice is civil injunction because it serves as a legal order that requires an individual to stop a specific action or to refrain from continuing a behavior that is deemed harmful or unlawful. In essence, a civil injunction is typically issued by a court to prevent someone from engaging in activities that could cause injury or damage to another party. This type of order is often sought in cases where monetary damages would not be sufficient to address the harm caused, thus emphasizing its role in mandating a pause or change in behavior.

In contrast, the other options have different purposes: a subpoena ad testificandum compels a person to testify in a legal proceeding but does not direct action beyond that context; a criminal charge is a formal accusation that someone has committed a crime and initiates legal proceedings, rather than directly ordering an action; and a reprimand typically serves as a form of disciplinary action without the legal authority to mandate changes in behavior.