This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
Macromolecules in Dental Resin is attached by: 
Select and explain. 
A. Covalent bonds, B. Sonic bonds, C. Vander Wall's Forces, D. Hydrogen Bonds
A: Covalent bonds
Answer: A: Covalent bonds 
Explanation: None