Under what condition are two or more hoses on a retail LPG device allowed?

The correct option focuses on the presence of a three-port two-way valve or a similar system, which is essential for safely managing the flow of LPG from multiple hoses. This condition ensures that each hose can be independently controlled and that the system's operation adheres to safety standards. The presence of such a valve reduces the risk of backflow or incorrect pressure levels in the hoses, which is critical for maintaining the integrity of the LPG system and preventing hazardous situations.

While other options may seem reasonable, they do not address the core safety concerns associated with the operation of multiple hoses. Having hoses of the same length, equal diameter, or using the hoses solely for vapor doesn't inherently ensure that the system operates safely or efficiently. Without proper management through appropriate valves, the risk of issues such as pressure imbalance remains significant.