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: Biochemistry
The two strands of DNA are held together by 
Select and explain. 
A. Van-der-Waal bond, B. Hydrogen bond, C. Covalent bond, D. Ionic interaction
B: Hydrogen bond
Answer: B: Hydrogen bond 
Explanation: Two strands of DNA are held together by hydrogen bonds between complementary pairs of bases.