John steps outside and observes that clouds have started to form in the sky, and it looks like it could rain. Which of the following is the best way to explain why the clouds have formed? A) The temperature of the air is below zero.
B) There is a low amount of moisture in the air.
C) The warm, wet air in a low pressure system has risen up and cooled down.
D) The wind is traveling at a slow speed.

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?

Blank is a rock with a find dark texture that makes up the oceanic crust

Which of these outcomes is a negative impact of postindustrial societies on the environment? a. nomadic ways b. overpopulation c. overgrazing d. resource renewal