Researchers want to use eDNA to look for an invasive species in a waterway. Which of the following steps should they do first?
O A. Isolate eDNA from water samples taken from the waterway.
B. Compare the eDNA with a positive control.
C. Cut the eDNA into fragments of different sizes.
D. Sort the eDNA into bands on a gel.

Answer is A I just did it

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?