During the process of gene amplification using $PCR$,if very high temperature is not maintained in the beginning,then which of the following steps of $PCR$ will be affected first?

Consider the following statements about $PCR$:
$I.$ Polymerase Chain Reaction $(PCR)$ is a technique of synthesizing multiple copies of the desired gene in vitro.
$II.$ This technique was developed by Kary Mullis in $1985$.
$III.$ $A$ single $PCR$ amplification cycle involves three basic steps: denaturation,annealing,and extension.
Which of the statements given above are correct?

$PCR$ is used for:

The diagram below refers to $PCR$. Identify the steps $A, B$ and $C$ and select the correct option.

Plant cells are bombarded with high-velocity micro-particles of ........... coated with $DNA$ in a method known as gene gun.

Which of the following is not the application of $\text{PCR}?$