Respuesta :

Explanation:

Watson and Crick's model is composed of two anti parallel strands that are connected by hydrogen bonds between nitrogenous bases. Hydrogen bonds form between adenine and thymine and between cytosine and guanine. The  multiple strands of DNA double helix are  joined combinedly by hydrogen bonds between nitrogenous bases on opposite strands. Every pairs of the bases present the flat, which further makes a "rung" on the ladder of the DNA molecule.