Why is still water an ideal environment for the formation of mold and cast fossils? Sediment builds up over organisms.
Sediment turns organisms into rock.
Hard tissue decays under sediment.
Soft tissue is preserved under sediment.

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).

answer denitrification;