Help me pls I'm. struck

Why my Ursina is not installing ​

The atomic nucleus made up from protons (yellow) and neutrons (blue) and held together by nuclear forces. nuclear forces (also known as nuclear interactions or strong forces) are the forces that act between two or more nucleons. they bind protons and neutrons (“nucleons”) into atomic

Answer; carbon monoxide (co);

The answer will be c

Answer earth,water,fire and air;