Why would lac z gene be fused to coding sequence of chain $A$ and $B$ in plasmids of $E.$coli?

In recombination vector used is

The critical research areas of biotechnology are

$I$. providing best catalyst as improved organism, usually a microbes or pure enzyme

$II$. creating optimal conditions by engineering for a catalyst to act

$III$. down stream processing technologies

$IV$. Multiple Ovulation Transfer Technology $(MOET)$

Which of the statements given above the correct?

Which enzyme was targetted during the first clinical gene therapy given in $1990$ to a four year- old girl?

Consider the following statements

$I$. Transgenic animals are more sensitive to the toxic substance than non-transgenic animals

$II$. Useful biological products can be produced by introducing into transgenic animals the portion of $DNA$ which codes for a particular product

$III$. Brazzein is a protein produced by a west African plant, Pentadiplandra brazzeana which is approximately $2000$ time as sweet as sugar

Which of the statements are given above are correct?