A comet is best known for its visible tail that can even be seen with the naked eye as comets, like Halley’s Comet has a tail at some points during its orbit, but not at other points?

A. As the comet nears the sun, the temperature rises, which causes the tail to appear.

B. As the comet nears the sun, the temperature falls, which causes the tail to appear.

C. As the comet moves away from the sun, the temperature rises, which causes the tail to appear.

D. As the comet moves away from the sun, the temperature falls, which causes the tail to appear.

Calvin ate a candy bar, which caused his body's blood glucose levels to become unbalanced. his body responded by initiating a feedback mechanism to return his body to homeostasis. place the steps of this feedback mechanism in order, starting with the blood glucose imbalance that occurred after calvin consumed the candy bar. a) calvin's blood glucose levels decreased. b) calvin's pancreas stopped secreting insulin. c) calvin's body cells started to take up glucose and store it as glycogen. d) calvin's blood glucose levels increased. e) calvin's pancreas started secreting insulin.

Which kingdom includes some organisms that have no nucleus and can live in an environment with an extremely high salt content

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?