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

(N/A) $PCR$ stands for Polymerase Chain Reaction. It is a technique used to amplify a specific segment of $DNA$ in vitro. Each cycle of $PCR$ consists of three main steps:
$A$: Denaturation: The double-stranded $DNA$ is heated to a high temperature (about $94-98^{\circ}C$),which causes the two strands to separate into single-stranded $DNA$.
$B$: Annealing: The temperature is lowered (typically $50-65^{\circ}C$) to allow the two oligonucleotide primers to bind (anneal) to their complementary sequences on the single-stranded $DNA$ templates.
$C$: Extension: The temperature is adjusted (usually $72^{\circ}C$) to allow the thermostable $DNA$ polymerase (e.g.,$Taq$ polymerase) to synthesize a new $DNA$ strand by adding nucleotides to the primers,using the original $DNA$ as a template. This process is repeated for many cycles to achieve exponential amplification of the target $DNA$ segment.