Through which atp-generating mechanism can long-lasting muscle contractions be sustained?

Oxidative Metabolism

Explanation:

Long-lasting muscle contractions can be sustained through oxidative metabolism (a mechanism that acts as the dominant source of energy for skeletal muscle)

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).