Which of the following is a good sign of an approaching earthquake?

The selection of volcanic eruption as a sign of an approaching earthquake is based on the geological relationship between the two phenomena. Earthquakes often occur in tectonically active regions where tectonic plates meet, and volcanic activity can signal disruptions in the Earth's crust that may also lead to earthquakes. Therefore, the presence of a volcanic eruption might indicate significant geological activity in the area, which can sometimes precede seismic events.

In contrast, strong winds, a sunny day, or traffic do not provide meaningful information about seismic activities. Weather conditions such as wind and sunshine are largely unrelated to the occurrence of earthquakes, as are typical human activities like traffic. These factors do not reflect the geological processes associated with seismic events and thus are not reliable indicators of an earthquake's approach.