A nebula starts to collapse because of

This photograph shows the Orion Nebula, an interstellar cloud in which star systems - and possibly planets - are forming. Our own solar system presumably formed as gravity caused the collapse of a similar large cloud of gas. The piece of cloud that formed our Solar System is known as the solar nebula.

Explanation:

d is the correct answer.

b is incorrect because it makes food by itself

c is incorrect because us humans don't know how to produce their own food using the sun like plants.

a is incorrect because consumers can depend on carnivores for eating food for consumers to eat the dead organism. same thing with omnivores.

here are five steps to a strong outline:

choose your topic and establish your purpose. a lot of writers struggle to define the initial focus for their paper.

create a list of main ideas. this is the brainstorming part of the writing process.

organize your main ideas.

flush out your main points.

review and adjust.