Which of the following are important aspects of nucleic acids that lead to the formation of the DNA double helix.(Select all that apply.)a. The phosphate backbone of each polynucleotide chain is relatively hydrophilic and sits on the outside of the helix.b. Water bridges complementary bases, causing them to associate in pairs.c. Complementary bases form two or three hydrogen bonds.d. DNA bases are relatively hydrophobic and sit at the core of the helix.