Read this excerpt from "Why Are They Called Black Holes?" Within a circular boundary of about fifty miles from the black hole center, gravity is so strong that massless light cannot escape its pull. This boundary is called the "theoretical event horizon." Imagine observing a black hole from galaxies away. Light can be seen around the event horizon but not within it. The universe is filled with dim light drifting all around, but absolutely no light can be seen inside a circular event horizon. Therefore, the area inside is called a "black hole."

Based on this excerpt, which conclusion is most likely true about black holes?

Even though there is light inside a black hole, it is not visible.
Even though a black hole has gravity, there is nothing inside a black hole.
A black hole can only be observed or detected at a short distance.
A black hole only releases light that appears black to the eyes.