In agarose gel electrophoresis,$DNA$ molecules of different lengths are separated on the basis of their

$A$ : $Pst I$ generates single-stranded overhanging stretches in $DNA$ after digestion that facilitate ligation.
$R$ : These short extensions can form hydrogen bonds with their complementary counterparts,which are then sealed by $DNA$ ligase to form phosphodiester bonds.

The second part of the name of a restriction endonuclease is derived from the:

$A$ - $amp^R$ has recognition sites for $Pvu I$.
$R$ - $tet^R$ gene has no recognition site for $Hind III$.

Choose the correct pair from the following:

The first restriction endonuclease type $II$,$...A..$,was isolated by Smith,Wilcox and Kelley from $...B...$ bacterium. It was found to cut $DNA$ molecules at a particular point by recognizing a specific sequence of six base pairs,known as the $...C....$. Here $A, B$ and $C$ can be: