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?

Subduction zones form when an oceanic plate collides with another oceanic plate or continental plate. the continental crust is lighter and less dense than oceanic crust. continental crust's density is approximately 2.7 grams per cubic centimeter. oceanic crust is thinner and the average density is about 3.3 cubic centimeters. when the two crustal plates converge the oceanic plate always bends and subducts beneath a continental plate. once the oceanic crust subjects, the rocks are subjected to changes in heat and pressure. because of this, we would expect to find rocks in the area of a subduction. a) clastic b) igneous c) metamorphic d) sedimentary