Which statement about the use of independent variables in controlled experiments is correct? 1.
A different independent variable must be used each time an experiment is repeated.
2.
The independent variables must involve time.
3.
Only one independent variable is used for each experiment.
4.
The independent variables state the problem being tested.

Which zone within the open-ocean zone is home to the most organisms? deep zone surface zone intertidal zone transition zone

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?

Warmer ocean surface water would most likely be found near