The answer would be d) phenotype. The phenotype is the physical characteristic while the genotype is the combination of alleles from the parent--basically the part that you can't really see. The color of a flower is prominent, so that would be its phenotype. An organism's phenotype can also include certain behavioral characteristics as well, not just the way it looks! Hope this helped :)
Pollution is always a good way to go but you don't have to do air pollution you can do water pollution or both air and water pollution.
