Read the excerpt from A Black Hole is NOT a Hole. Have you ever watched the Sun set? After it sinks below the horizon, Earth blocks your view of it. Even though you know it’s still out there in space, you can’t see it. Any and all events on the Sun remain invisible to you for as long as it is below the horizon. If the Sun suddenly turned purple, you wouldn’t see it happen.

In a similar way, once an object enters the extreme gravity zone of a black hole, the object disappears from view. Even though nothing physically blocks our sight, once the object is beyond the boundary of the zone, we cannot see what happens to it. Events beyond the black hole’s "horizon” are invisible to us. Because of this visual effect, scientists named the boundary the "event horizon".

What similarity is explained in this excerpt?

The sun’s disappearance after sunset is similar to the way an object disappears near a black hole.
The sun’s temperature after sunset is similar to the way an object cools near a black hole.
The sun’s color after sunset is similar to the way an object changes color near a black hole.
The sun’s speed after sunset is similar to the way an object changes speed near a black hole.