Who discovered $PCR$ (Polymerase Chain Reaction)?

The prerequisites for the biotechnological production of antibiotics are:

$I. ... A...$ is the ability of a cell to take up foreign $DNA$.
$II.$ The cell is treated with a specific concentration of a divalent cation such as $... B...$ to increase the pore size in the cell wall.
$III.$ In $...C...$ method,recombinant $DNA$ is directly injected into the nucleus of an animal cell.
The most appropriate option regarding $A, B$ and $C$ is:

Production of a human protein in bacteria by genetic engineering is possible because

In the $PCR$ technique,how are the two strands of $DNA$ separated?

Which of the following is $NOT$ an application of $PCR$ (Polymerase Chain Reaction)?