How can purified $DNA$ be precipitated from a solution after appropriate treatment?

If a recombinant $DNA$ bearing a gene for ampicillin resistance is transferred into $E. coli$ cells and the host cells are spread on agar plates containing ampicillin,then:

In the purification process of recombinant $DNA$ technology,what does the addition of chilled ethanol precipitate?

Identify and explain steps $A$,$B$,and $C$ in the $PCR$ diagram given below.

Can you think and answer how a reporter enzyme can be used to monitor transformation of host cells by foreign $DNA$ in addition to a selectable marker?

Which statements are correct for gel electrophoresis to separate $\text{DNA}$ fragments?
$(a)$ $\text{DNA}$ is a negatively charged molecule and so it is loaded on the gel towards the anode terminal.
$(b)$ $\text{DNA}$ fragments travel along the surface of the gel whose concentration does not affect the movement of $\text{DNA}$.
$(c)$ Smaller the size of $\text{DNA}$ fragments,larger is the distance it travels through it.
$(d)$ Pure $\text{DNA}$ can be visualized directly by exposing it to $\text{UV}$ radiation.