You are studying an individual with very low levels of insulin in her blood. further analysis indicates that cells of her pancreas are producing normal levels of this protein, but it is accumulating in the cytoplasm rather than being secreted from the cells. which hypothesis makes the most sense to explain this observation?

a small deletion occurs in the nucleotide sequence at the aminoterminal of the gene in the signal sequence

Explanation:

A  deletion in the sequence of nucleotide that code for the  small signal sequence responsible will affect the release of insulin outside the cells because the signal sequence is responsible for carrying the insulin outside the cells. The cells of pancreas are producing the insulin normally but due to mutation in the signal sequence it can not  release out of the cells and accumulate inside the cells.

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).