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Answer:
4
Explanation:
Carbon has four valence electrons, so it can achieve a full outer energy level by forming four covalent bonds. When it bonds only with hydrogen, it forms compounds called hydrocarbons. Carbon can form single, double, or triple covalent bonds with other carbon atoms.
The answer is the pigment red
The immune system works with the digestive tract to help protect you from infection by these potential invaders. Your immune system also depends upon cells to kill invading organisms, and chemicals that don't require the involvement of cells at all, but which are simply toxic to bacteria and viruses. Acid in the stomach does the same thing.