You are telling your friend that organic molecules are all made up of carbon backbones with hydrogens. She doesn't understand how there can be so many different organic molecules if they all are made up of the same basic components. You explain that organic molecules

A) actually all have the same structure but differ in the number of electrons.
B) are different because of the different types of hydrogen bonds that form.
C) vary because they possess different isotopes of carbon.
D) vary because they possess different functional groups.