select the correct answer from the list.

Gravity pulls matter together or causes pressure change.

To form a nebula, gravity pulls matter together.

To select the correct answer from the list, we need to understand the process of forming a nebula. A nebula is a large cloud of gas and dust in space. The formation of a nebula involves the forces of pressure, gravity, and heat.

Gravity is the force that pulls matter together, causing it to clump and form structures like stars and galaxies. In the context of forming a nebula, gravity is responsible for pulling the matter together.

On the other hand, heat and pressure are not the primary forces involved in the formation of a nebula. Heat is typically generated within a nebula due to the compression of matter under gravity, but it is not the force responsible for pulling matter together. Pressure, too, can be present within a nebula, but it is not the cause of matter clumping together.

Therefore, the correct answer is: Gravity pulls matter together.