Transposons can be used during which one of the following?

Golden rice

$I$. It is a transgenic variety of rice

$II$. It contains a goods quality of $\beta$-carotene (provitamin-A)

$III$. $\beta$-carotene is a principal source of vitamin- $A$

$IV$. The grains of the rice are yellow in colour due to $\beta$-carotene. The rice is commonly called golden rice

Which of the statements given above are correct?

Given below are two statements:

Statement $I$ : Bt toxins are insect group specific and coded by a gene cry $IAc$.

Statement $II$ : Bt toxin exists as inactive protoxin in B. thuringiensis. However, after ingestion by the insect the inactive protoxin gets converted into active form due to acidic $\mathrm{pH}$ of the insect gut.

In the light of the above statements, choose the correct answer from the options given below:

The bacterium Bacillus thuringiensis is widely used in contemporary biology as

The scientific process by which crop plants are enriched with certain desirable nutrients is called