Under which conditions is passing considered unlawful and unsafe?

Passing is considered unlawful and unsafe on hills, curves, and at intersections or railroad crossings because visibility is often limited in these areas. When driving on a hill or around a curve, it is difficult to see oncoming traffic, which increases the risk of a collision when attempting to pass. Similarly, at intersections or railroad crossings, passing can impede the flow of traffic or create dangerous situations where vehicles may be entering or crossing paths at high speeds. These conditions require heightened caution, and the laws are specifically designed to prevent dangerous behavior that could lead to accidents. In contrast, the other options describe scenarios where passing may be permissible under the right circumstances.