Fixation
Nitrogen is converted from atmospheric nitrogen (N2) into usable forms, such as NO2-, in a process known as fixation. The majority of nitrogen is fixed by bacteria, most of which are symbiotic with plants. Recently fixed ammonia is then converted to biologically useful forms by specialized bacteria
A testable question is B. If a plant is turned upside down, which way will the roots grow?
The other options are incorrect because you cannot create some kind of experiment to prove them right or wrong.
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Answer:
It is recommended to get a flu shot every year as the flu shot only provides protection against the flu for about 6 months. An individual's immune protection from the vaccination declines over time, so they need a new vaccine for optimal protection. In addition, flu viruses evolve and mutate very quickly. New flu vaccines are administered every year to address the rapidly adapting flu virus.
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