Which of the following methods is used for the isolation of $DNA$?

Which one of the following statements is correct regarding gel electrophoresis?

It is used to detect $HIV$ in suspected $AIDS$ patient and detect mutations in genes in suspected cancer patient too.

Separated bands of $\text{DNA}$ in agarose gel electrophoresis observed under $\text{UV}$ radiation are stained with

Bioreactors are useful in

$I. ... A...$ 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: