Why are stirred-tank bioreactors specifically designed?

What are the temperatures required for the three steps of the Polymerase Chain Reaction $(PCR)$ shown below?
$P \quad \quad Q \quad \quad R$

$A$: To extract $RNA$ from tomato cells,it must first be treated with cellulase,protease,and then deoxyribonuclease.
$R$: Deoxyribonuclease will digest $DNA$ while $RNA$ will be intact.

The preparatory phase before fermentation is known as:

The cutting of $DNA$ by restriction endonucleases results in the fragments of $DNA$. These fragments can be separated by a technique known as ......

Which of the following statements are correct with respect to $DNA$ separation, isolation and visualization?
$A$. The cutting of $DNA$ is done by molecular scissors.
$B$. The $DNA$ fragments separate according to their size in an agarose gel, upon electrophoresis.
$C$. The separated $DNA$ fragments can be seen without staining when exposed to $UV$ light.
$D$. The separated $DNA$ fragments, when stained with ethidium bromide, can be seen in visible light.
Choose the correct answer from the options given below: