What does $Bt$ stand for?

In $Bt$ cotton,the toxin is coded by a gene named ...........

Given below are two statements:
Statement-$I$: In $\text{pBR}-322$,the restriction site of $\text{BamHI}$ is present on the $\text{Ampicillin}$ resistance gene.
Statement-$II$: $\text{RNAi}$ technique was used in the formation of nematode-resistant plants.
In the light of the above statements,choose the correct answer from the options given below:

What is true about $Bt$ toxin?

What is the main characteristic observed in $BT$ cotton?

$Bacillus \text{ } thuringiensis$ produces ......... that kill certain insects such as .........