Assertion $(A)$: The denaturation of proteins can destroy all $1^{\circ}, 2^{\circ}$ and $3^{\circ}$ protein structures.
Reason $(R)$: Curdling of milk is due to denaturation of proteins.
The correct option among the following is

• A
  $(A)$ is true,$(R)$ is true and $(R)$ is the correct explanation for $(A)$
• B
  $(A)$ is true,$(R)$ is true but $(R)$ is not the correct explanation for $(A)$
• C
  $(A)$ is true but $(R)$ is false
• D
  $(A)$ is false but $(R)$ is true