Which enzyme is used to join foreign $DNA$ to a plasmid?

In plants,the tumour inducing plasmid $(Ti)$ of $Agrobacterium$ $tumefaciens$ is used as a cloning vector. This statement is

Identify the desirable characteristics for a plasmid used in $rDNA$ technology from the following.
$A$. Ability to multiply and express outside the host in a bioreactor.
$B$. $A$ highly active promoter
$C$. $A$ site at which replication can be initiated
$D$. One or more identifiable marker genes
$E$. One or more unique restriction sites.

In the nomenclature of the enzyme $Restriction$ $Endonuclease$,what does the Roman numeral indicate?

Nowadays, which of the following are known as "magic circles"?

In addition to $Taq$ polymerase enzyme,which other thermostable $DNA$ polymerases have been isolated to be used in Polymerase Chain Reaction $(PCR)$?