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

Restriction enzymes should not have more than one site of action in the cloning site of a vector. Comment.

$Taq$ polymerase is isolated from a bacterium,$Thermus$ $aquaticus$.

Select the appropriate option for $Agrobacterium$ $tumefaciens$.

$Taq$ polymerase used for the amplification of $DNA$ is associated with .........

Refer to the following statements for agarose-gel electrophoresis :
$(a)$ Agarose is a natural polymer obtained from sea-weed.
$(b)$ The separation of $DNA$ molecules in agarose-gel electrophoresis depends on the size of $DNA$.
$(c)$ The $DNA$ migrates from negatively-charged electrode to the positively-charged electrode.
$(d)$ The $DNA$ migrates from positively-charged electrode to the negatively-charged electrode.
Choose the most appropriate answer from the options given below :