Why is it unwise to rely solely on another driver's signal lights?

Answer: B — The signal may have been left on from an earlier turn

Relying solely on another driver's signal lights is unwise because signals may sometimes be misleading or inaccurate. One reason is that a driver may have left their signal on after making a turn, creating confusion for other drivers. This situation can lead to misinterpretation of the driver's intentions, resulting in dangerous situations on the road. While it is true that some drivers may forget to signal or may not be paying full attention, the reliability of the signal itself is crucial. Moreover, malfunctioning signals can also contribute to the ambiguity in signaling. Thus, while all these factors play a role in road safety, the specific concern about a signal being left on highlights the importance of actively observing the actions of other vehicles rather than relying solely on their signals for safe driving decisions.