Answer the following question given this paragraph: 

Scientists think the solar system formed from a big cloud of gas and dust, called a nebula . This is the solar nebula hypothesis. The nebula was made mostly of hydrogen and helium. There were heavier elements too. Gravity caused the nebula to contract ( Figure below ).


Q: Scientists think the solar system formed from a big cloud of gas and dust called what?

 Choices:

- comet

- supernova

- Oort cloud

- nebula

A:
nebula
