Question

nitrogenous bases are joined by which type of bond? covalent bonds polar bonds hydrogen bonds ionic bonds

Explanation:

Nitrogenous bases in nucleic acids (like DNA) form specific pairs. Adenine pairs with thymine (or uracil in RNA) and guanine pairs with cytosine. These pairs are held together by hydrogen bonds. Covalent bonds are involved in the sugar - phosphate backbone, not in joining nitrogenous bases. Polar bonds are a type of covalent bond based on electronegativity differences. Ionic bonds involve the transfer of electrons between atoms (not relevant here as nitrogenous base pairing is about hydrogen bonding).

Answer:

C. hydrogen bonds