Read the excerpt from A Black Hole is NOT a Hole. 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.

Which word signals that a comparison is being made?
A) extreme
B) object
C) gravity
D) similar