Although there are over 100 elements in the universe, organic matter usually contains a limited number of these elements and always includes the element

Although there are a little more than 100 different elements in the world, only a small number comprise a majority of the different systems on Earth. The elements that make up rocks and minerals of solid Earth include silicon, oxygen, iron, magnesium, and other trace amounts of various elements. Living organisms are composed primarily of carbon, oxygen, and hydrogen. Other elements in living matter include calcium, nitrogen, phosphorus, potassium, and trace amounts of other elements. 

The answer is letter c