Which of the following is an example of exigent circumstances?

The example of exigent circumstances in the context provided is the scenario involving the smell of natural gas. Exigent circumstances refer to situations where law enforcement officers are allowed to act without a warrant due to an immediate need to prevent harm, destruction of evidence, or to secure a suspect. In this case, the smell of natural gas creates an urgent threat to public safety, prompting officers to take immediate action to mitigate potential danger to individuals nearby.

When officers detect a potentially hazardous situation, like a gas leak, they must act swiftly to ensure that no one is harmed, which justifies bypassing the usual requirements for a warrant. This represents a classic example of exigent circumstances, where the immediacy of the threat overrides the need for prior judicial approval.

The other options do not demonstrate exigent circumstances as they involve either planned actions, like a police raid or issuing a search warrant, or routine procedures, such as a crime scene investigation, which do not require immediate action in the face of imminent danger.