The tumor inducing (Ti) plasmid has now been modified into a cloning vector which is no more pathogenic to the plants but is still able to use the mechanisms to deliver genes of our interest into a variety of plants because Ti plasmid has been modified by :

1. Deleting tumor forming genes
2. Adding tumor forming genes
3. Deleting endonuclease
4. Adding genes resistant to endonucleases

The correct option is A Deleting tumor forming genes
The tumor inducing (Ti) plasmid of Agrobacterium tumefaciens has now been modified into a cloning vector which is no more pathogenic to the plants but is still able to use the mechanisms to deliver genes of our interest into a variety of plants because Ti plasmid has been modified by deleting tumor forming genes.

So, once a gene or a DNA fragment has been ligated into a suitable vector it is transferred into a bacterial, plant or animal host (where it multiplies).

So, the correct answer is "option D"