when a person has heartburn acidic juices enter the esophagus and cause a burning sensation. where do these acidic juices come from?

Stomach

Explanation:

The acids are gastric acids.

Hope this helps! :)

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).