"i think the climate is changing," ben's father said. "every summer there are more and more hurricanes." ben's mother did not agree with him. ben had an idea. they could track the number of hurricanes that coming summer and compare the number to past summers. what would be a testable question for ben's hurricane research? a) is the climate onearth changing? b) how many hurricanes will there be this year? c) is the number of hurricanes increasing each year? d) the number of hurricanes is increasing year after year.

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?