Biotechnology has resulted in the formation of food crops that are resistant to herbicides. how was this most likely accomplished?

a. continually applying herbicides to the plants until they developed a tolerance to them
b. halting the use of herbicides on the food crops so that they could build a tolerance to them
c. inserting genes resistant to the herbicides into the dna of the plants
d. placing a portion of the plant’s genes into the herbicides