Consider the following statements about $PCR$:
$I.$ Polymerase Chain Reaction $(PCR)$ is a technique of synthesizing multiple copies of the desired gene in vitro.
$II.$ This technique was developed by Kary Mullis in $1985$.
$III.$ $A$ single $PCR$ amplification cycle involves three basic steps: denaturation,annealing,and extension.
Which of the statements given above are correct?

• A
  $I$ and $II$
• B
  $I$ and $III$
• C
  $II$ and $III$
• D
  $I, II$ and $III$