Final answer:
Cutting the plasmid and foreign DNA with the same restriction enzyme ensures the right border of the T-DNA region is released and transferred.
Step-by-step explanation:
In order to ensure that the right border is cut first and that the T-DNA region is transferred, the T-DNA is cut by a restriction enzyme. This process involves cutting the plasmid containing the T-DNA and the foreign DNA with the same restriction enzyme. The restriction enzyme recognizes a specific sequence of DNA called a restriction site, which occurs only once in the plasmid. By cutting at this site, the right border of the T-DNA region is released, allowing it to be transferred to the plant cell.