Answer: 
The correct answer is option A. covalent bond. 
Explanation: 
Bonding between two carbon atoms is a Covalent bond that is also called a carbon-carbon bond. The covalent bond is also known as a molecular bond that forms by the sharing of electron pairs between atoms. 
The most common bond between carbon-carbon atom is a sigma covalent bond that involves one electron from both atoms. The three major covalent bonds are the single, double and triple bond. 
Thus, the correct answer is option A. covalent.