What reflects the capability of drawing attention to a stop using a fixed signal?

Answer: B — controlled signal

The choice that accurately reflects the capability of drawing attention to a stop using a fixed signal is the controlled signal. Controlled signals are specifically designed to convey information to train crews, such as whether they should stop or proceed. These signals are part of the fixed signal system on railroads and play a crucial role in ensuring the safety and regulation of train movement. Contrarily, the other options serve different functions. Block limits indicate the boundaries of signal blocks, but they do not directly inform train crews about stopping. Cab signals provide indications to the locomotive engineer regarding speed limits and upcoming signals, rather than directly signaling stops. Distant signals are positioned ahead of a controlled signal to alert the train crew of the state of the upcoming controlled signal but do not independently indicate a stop; their role is more about preparing the crew for what is ahead in terms of signals. In this context, the controlled signal stands out as the most effective form of fixed signal for drawing attention to a stop, making it the correct choice.