Final answer:
To report something suspicious or an emergency, you should call 911. This number connects you instantly to the necessary emergency services and ensures quick response.
Step-by-step explanation:
The number you should call to report something suspicious or an emergency is A) 911. This number is designated for emergency services in many countries, including the United States, and is intended for situations that require immediate attention from the police, fire department, or medical services. When you dial 911, a dispatcher will answer and ask you for details about the emergency, so they can send the appropriate services to your location.