Under what circumstances can you arrest someone according to the law?

The correct choice is based on the legal principles surrounding the authority to arrest an individual. An arrest can be made when law enforcement officers have probable cause to believe that a crime has occurred or is occurring. This means that if a crime has been committed, there is a direct basis for making an arrest because the officer has evidence or reason to believe that the individual is responsible for that offense.

Furthermore, the ability to arrest someone based on suspicion of an imminent crime relates to the concept of "prevention" in law enforcement. If an officer suspects, based on reasonable grounds, that a person is about to commit a crime, they may act to arrest that individual in order to prevent the crime from happening. This allows law enforcement to intervene proactively rather than reactively.

Option A aligns with the principle that an arrest can occur once a crime has been confirmed, while option B addresses the necessity of acting upon credible suspicion of a crime in progress or about to occur. Therefore, the combination of these two principles effectively encompasses the legal basis for making an arrest, leading to the selection of the answer that combines both circumstances.