[OU.03] A star is moving away from Earth. An astronomer plans to measure the distance of the star from Earth by observing the blue shift in its spectrum. Which of these statements best explains why the astronomer's method of measuring the star distance is inappropriate? The spectral shift of moving stars cannot be observed. Common instruments cannot measure the blue shift accurately. A blue shift can be observed when the star moves towards Earth. Rate of motion of stars cannot be matched with the rate of measuring distances.

Which component in a graph indicates an independent factor? a. y-axis b. x-axis c. scale

Why has two different alleles for the same trait?

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?