Question

what is a nebula?
o the core of a massive star
o a cloud of gas and dust in space
o a swirling disk with a lot of gravity
o the debris remaining after a supernova

Explanation:

A nebula is an interstellar cloud made up of gas (mostly hydrogen and helium) and dust. It is not the core of a massive star, nor is it just the debris from a supernova (though some nebulae can form from supernova remnants), and it's not a swirling disk with a lot of gravity (which is more characteristic of an accretion disk around a black - hole or forming star).

Answer:

B. a cloud of gas and dust in space