Wmany grams of cobalt-60 how many grams of cobalt-60 will remain after three half-lives? A. 180 g
B. 2.50 g
C. 1.25 g
D. 30 g

that scientist would be robert hooke

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).