Scale is the proportion used in determining the relationship between an actual object and a model of the object.

For example, real estate developers often make models of shopping centers. If a model of a store has a scale of 1 centimeter equaling 20 feet, what is the actual length of a store that measures 5 cm in length on the model?
A.
100 feet
B.
50 feet
C.
200 feet
D.
20 feet

Astudy by solloch and et. al., in 2017, gives the map above which shows the frequency of alleles with a ccr5-delta32 mutations over 87 different countries. this mutation deletes the presence of a co-receptor (ccr5) on the outside of human t-cells (lymphocytes). some viruses, such as the one responsible for the black death and human immunodeficiency virus (hiv), require this receptor for attachment to host cells during the infection process. the black death was an epidemic that passed over northern europe during the 14th century killing nearly 60% of europeans. according to this information, which explanation best explains why northern europeans show a greater immunity for hiv than some other parts of the world?