Data from single-cell recordings are typically visualized with a raster plot in which: a) time (ms) is depicted horizontally and trials are depicted vertically, where each trial corresponds to a different neuron or set of neurons b) time (ms) is depicted horizontally and trials are depicted vertically, where all trials correspond to the same neuron or set of neurons c) time (ms) is depicted vertically and trials are depicted horizontally, where each trial corresponds to a different neuron or set of neurons d) time (ms) is depicted vertically and trials are depicted horizontally, where all trials correspond to the same neuron or set of neurons

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?