Select the correct sequence of steps in $PCR$.

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:

Select the incorrect statement regarding the continuous culture system.

Which of the following steps is/are catalysed by $Taq$ polymerase in a $PCR$?

Which method is used to introduce $r-DNA$ directly into the nucleus of an animal cell?

Which of the following cannot be used for direct gene transfer?