Question

question 18 of 19 > the horsehead nebula is one of the most recognizable dark nebulae in the sky. why is the nebula dark? it is a cloud that is so cold that it emits no electromagnetic radiation. it is a cloud that is practically empty and therefore does not emit any electromagnetic radiation. it is a cloud of gas and dust around a black hole. it is a dense molecular cloud that blocks the visible light from the h ii region behind it.

Explanation:

The Horsehead Nebula is dark because it is a dense molecular cloud that obscures the visible - light from the H II region behind it. It is not because it is extremely cold and emits no radiation, nor is it an empty cloud, and it is not a cloud around a black hole.

Answer:

It is a dense molecular cloud that blocks the visible light from the H II region behind it.