Walter Sutton discovered that chromosomes are the basis of heredity and this explained the segregation of alleles in Mendel's law of segregation. Basically alleles and chromosomes in Mendel's explanation are the same thing.
The structure of the skin is an effective barrier against bacteria. The multiple layers of epidermis, while can be invaded by foreign organisms, has a high turnover rate which means it is constantly shedding, therefore even the bacteria is shed protecting the body. Lastly, the skin's lipids maintain an acidic pH which slows and stops growth and replication of bacteria.
Natural variation provided the phenotypes that natural selection then acted on, over time causing evolution
Answer: I think the answer is A. because I remember doing it when we were still in school I chose A. and I got a 100%.