when a plastic rod is rubbed with a woollen cloth, the rod becomes negatively charged. this is because the negatively charged electrons move onto the rod, but how am I supposed to know which electrons move to what rod in a different example???

the answer is :

the last one: artificial selection/genetic engineering

plant breeding is modifying the genetic composition of the plant - but this isn't cloning (which is specifically introducing a gene into a genome). but you are artificially selecting for the phenotype that you want.

the second one is literally genetic engineering - the gene would have been cloned first and then inserted or genetically engineered into the new plant cell (the cotton).