$A$ probe is used in which stage of genetic engineering?

$A$: 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.

Select the correct statement from the following.

Consider the following figure of a stirred-tank bioreactor and identify $A, B, C$,and $D$.

Refer to the following statements for agarose-gel electrophoresis:
$(a)$ The $\text{DNA}$ fragments resolve according to their size.
$(b)$ The separated $\text{DNA}$ fragment can be visualised only after staining with ethidium bromide followed by exposure to $UV$ radiation.
$(c)$ $\text{DNA}$ is always loaded into the well.
$(d)$ The smallest fragment of $\text{DNA}$ is near the well.
Choose the correct statements:

Study the given figure carefully and select the correct statements regarding this.
$I.$ It represents typical agarose gel electrophoresis showing differential migration of $DNA$ fragments.
$II.$ Lane $1$ contains undigested $DNA$ fragments.
$III.$ Lanes $2$ to $4$ contain digested $DNA$ fragments.
$IV.$ Smallest $DNA$ bands are present at $(A)$ position and largest $DNA$ bands are present at $(B)$ position.