Which enzyme is responsible for joining two fragments of $DNA$?

What are plasmids? Describe their role in bacteria.

The chemical knives of $DNA$ are:

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:

Which of the following is an $E. coli$ cloning vector?

The term "Molecular Scissors" refers to