Which of the following can cause a monitor to transfer the intersection into flash mode?

Answer: B — Loss of power to the controller

A monitor transferring an intersection into flash mode is typically a safety measure to manage traffic flow under certain conditions. Loss of power to the controller is a critical situation that can lead to this response. When power is lost, the traffic signals can no longer operate as intended, leading to a default state, which is often flash mode. This mode helps in alerting drivers to potential hazards at the intersection since the signals are not functioning normally. Other situations such as intervention by traffic personnel or controller maintenance may influence the operation of traffic signals but do not inherently lead to a system-wide failure that necessitates switching to flash mode. Increased traffic flow also does not trigger flash mode; instead, systems are usually designed to handle variations in traffic volume without requiring a fallback to flash mode unless there's a fault or operational issue.