This signal aspect means that a train operator may pass expecting to find the next signal on the main route as:

The correct answer indicates that when a train operator sees a yellow or green signal aspect, they can proceed with the expectation that the upcoming signal will indicate a safe condition on the main track.

A green signal specifically means that the track ahead is clear, allowing the train to continue at full speed. On the other hand, a yellow signal serves as a caution, warning the operator that the next signal is likely to be either red or yellow, indicating the need for reduced speed or preparation to stop.

This combination of yellow and green streamlines operations by informing the train operator that while one aspect allows for continued movement, they should still be prepared for potential changes ahead, thus enhancing safety and efficiency on the rails. The other combinations listed do not align with standard signaling protocols, rendering them incorrect.