Each hereditary trait corresponds to O a sequence of nitrogen bases
O a step on the ladder
an arrangement of nucleotides
O an enzyme

yes, because even though a theory has a  lot of evidence to support it, it is not always true

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).