Which one of the following statements about $Agrobacterium \;Ti\; plasmid$ is $CORRECT$?
- $Vir$ genes are located within the $T-DNA$ segment
- Phytohormone biosynthesis genes are located outside the $T-DNA$ segment
- Opine catabolism genes are located within the $T-DNA$ segment
- Opine biosynthesis genes are located within the $T-DNA$ segment