A student designs an investigation to evaluate the effect of water acidity on the growth rate of potted spruce trees. What should be the independent variable in
the student's investigation?

Acar traveld with an average speed of 60 miles per hour for 2 hours. how far did it travel

What if the yeast were extremely active and produced more than 100ml gas. would you know? why/why not

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?