Answer :
A is the correct answer.
Chemical bonds can be classified as strong or weak. Van der Waals bonds (attractions) are weak and ionic or covalent bonds are strong. The bonds between bases, sugars and phosphates (answers B, C and D) are all covalent and are strong. The bonds between two bases, answer A, are weak van der Waals bonds.
Chemical bonds can be classified as strong or weak. Van der Waals bonds (attractions) are weak and ionic or covalent bonds are strong. The bonds between bases, sugars and phosphates (answers B, C and D) are all covalent and are strong. The bonds between two bases, answer A, are weak van der Waals bonds.