Which one of the following statements about gender differences in muscle size and strength is true?
a. men have a larger proportion of muscle mass in the lower body than do women.
b. women tend to lose inches and increase strength as a result of resistance training.
c. men are about 10% stronger in upper-body strength when compared to women.
d. androgen levels in women are about two times higher than in men.

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?