drag each phrase to indicate which flood mitigation technique it describes.

floodplain management

storm water management

elevated structures

-used mainly on the coast

-protects buildings in low-lying areas prone to floods

-raises structures above flood level

-reduces water runoff into streets, lawns, and other sites

-enhanced by the addition of urban green spaces

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?