The return of salmon to their own birthplace to breed is an example of
(a) habituation.
(b) a stimulus.
(c) operant conditioning.
(d) reasoned behavior.
(e) imprinting.

Ascientist and her team counted 200 individual deer in an area of 10 square kilometers. what is the population density?

The transport tubes for food coming down the plants are called?

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?