Which of the following is an example of the skeletal system interacting directly with the
respiratory system?

a the ribcage expands to allow air to enter the lungs.
b the muscles attached to bones contract to lift your leg.
c the marrow inside bones produces white blood cells.
d the vertebrae protect the spinal cord from injury,

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).