Which of the following statements best describes how a corn plant comes to produce the Bt toxin?
A. The Bt gene is inserted into each plant cell, one at a time, by using a bacterial plasmid.
B. The bacteria containing the Bt gene are sprayed onto the corn plants.
C. The Bt gene is inserted into one plant cell by using a bacterial plasmid.
D. The Bt gene is inserted into the soil and is taken into the corn plant through the roots.