Final answer:
Class 3 standpipe systems have 40mm & 65mm hose connections, which cater to firefighters and building occupants due to the balance of flow capacity and manageability.
Step-by-step explanation:
Class 3 standpipe systems are designed to accommodate the needs of both firefighters and building occupants. The correct answer to the question ‘Class 3 standpipe systems have?’ is c. 40mm & 65mm hose connections. These sizes allow for flexibility, with the 65mm typically used by firefighters due to its higher flow capacity, while the 40mm hose is more suitable for building occupants due to its manageability.