An experiment was conducted in which a purified protein from the body was exposed to a solution high in urea, and its tertiary structure was lost. When it was removed from the solution, the protein regained its original structure. Which of the following describes what is occurring when the protein is exposed to the solution high in urea?

A The side chains of the protein react with the urea, breaking bonds, which causes a conformation change.
B The sequence of amino acids rearranges in a toxic environment, which causes a conformation change.
C Urea reacts with the side chains of the protein sequence that causes a conformation change.
D The side chains of the protein react with urea, forming new bonds that cause a conformation change.