A client refers you to a friend who just purchased a commercial building and desires to purchase a policy in case of a tornado. What broad category of insurance would you recommend?

Property insurance is the correct recommendation in this scenario because it specifically covers physical assets, such as buildings and their contents, against risks like natural disasters, including tornadoes. When a client intends to protect a commercial building from potential damage due to tornadoes, property insurance is tailored to cover the structure itself and associated risks.

Casualty insurance, while also important, generally covers liability and does not primarily focus on direct damage to property. Tornado insurance, if it were a standalone category, would be a specialized form of property insurance, but it is not commonly recognized as a distinct type that stands alone in most insurance contexts. Multiple-line insurance could refer to a package that includes several types of coverage, which may not be specific enough for the particular risk of tornado damage to a building. Therefore, property insurance is the most direct and appropriate solution for the client's needs.