Why are the offspring of flowering plants genetically different from the parent plants?
a. sexual reproduction produces offspring with new combinations of genes.
b. sexual reproduction produces offspring with half the number of genes.
c. asexual reproduction produces offspring with twice as many genes.
d. asexual reproduction produces offspring with a variety of genes.

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?