If the molecules indicated by A are amino acids then the lin
     If the molecules indicated by (A) are amino acids, then the line in the figure indicated by (D) is  a hydrogen bond  a peptide bond  an active site  an R group 
  
  Solution
Peptide bond
If the molecules indicated by (A) are amino acids, then the line in the figure indicated by (D) is Peptide bond
In polypeptide chain, the amino acids are connected with each other through peptide bond and peptide bond is formed through a process of condensation, where water will be released out.

