Carbohydrates, fats, proteins: these organic molecules all have this element in common. this element can form multiple bonds, and it bonds with other elements as well as with itself. this element is
a. calcium.
b. carbon.
c. helium.
d. hydrogen.

The best answer is  B

Carbohydrates, proteins, lipids and nucleic acids are known as organic molecules, molecules of life. They are all built around chains of carbon atoms that are often quite long .

Each carbon atom can form strong, stable bonds with four other atoms at a time - these are usually oxygen, hydrogen, nitrogen, sulfur and phosphorous atoms. Carbon can also bond to other carbon atoms to form chains that are almost unlimited in length. This is what makes carbon so unique.

I believe the answer is linear :)