Lightning can combine nitrogen with other elements, or be fixed, in order to be used by plants. In what way is most of the fixed nitrogen made available for use by plants?
It is incorporated
into the
exoskeletons of
flying insects that
eat plants,
It is inhaled and
exhaled by birds.
It is carried by rain
to the soil.
It is moved by the
wind toward dry
areas.

Which of the following types of rock would most likely contain a fossil? slate granite lava rock limestone

Which best describes the scientific method? a. a path of clearly defined steps that must be followed in a particular order b. a possible answer to a scientific question based on knowledge or research c. the recipe for how to conduct an experiment that must be followed precisely d. the process of hypothesis and testing through which scientific inquiry occurs

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?