The element was poisonous to the first forms of life on earth until they evolved to take advantage of it by using cellular respiration. What is it? A. Hydrogen B. Nitrogen C. Oxygen D. Sulfur

The correct answer is C, oxygen. Oxygen was once harmful and used to cause harm to the DNA in primitive organisms.

Later on, the bacteria developed enzymes that prevented their DNA from damaging action of oxygen. Afterward, they evolved to use it for cellular respiration.