Carbon can also bond with other four atoms because of its outer shell (valence shell) that has four electrons. This is the reason why organic molecules can be so large because of this bonding. Suppose you have a compound of CCl4. You know that chlorine can only share 1 electron because 7 of its electrons are filled. Also, in carbon, it can only share 4 electrons because 4 of it are already filled. That is why carbon needs four chlorine to form CCl4. The answer is letter B.