Containers installed outside of buildings shall be located with respect to the adjacent containers, ____________, or group of buildings.

The correct answer focuses on the specific safety considerations associated with propane storage near structures. When locating containers outside of buildings, it is crucial to account for "Important Buildings," which typically refer to structures where a large number of people gather or where critical operations take place, such as hospitals, schools, and emergency service facilities.

The rationale behind prioritizing the distance from important buildings is to ensure maximizing safety and minimizing risk in the event of an incident involving propane. Regulations often stipulate barriers, distance requirements, and specific placement rules to protect these significant facilities and the individuals within them from potential hazards.

Other choices like highways, existing structures, and public areas might have their respective safety guidelines, but they do not encompass the specific concerns related to important buildings, which require stricter compliance due to their function and the number of people they serve.