What does a yellow unbroken (solid) line on the center line indicate?

A yellow unbroken (solid) line on the center line indicates that traffic moves in both directions, but it is a no passing zone. This design is meant to enhance safety by clearly signaling to drivers that passing is not permitted in this area. It helps prevent collisions that can occur when drivers attempt to overtake other vehicles in situations where visibility may be limited, such as on curves or hills. The solid line serves as a guideline for maintaining safe driving practices and ensuring that vehicles stay in their designated lanes.

The other options suggest various scenarios where passing is either allowed or directed, which contradicts the safety and regulatory purpose of the unbroken yellow line.