A ferromagnetic material is subjected to a strong magnetic field and afterward acts as a permanent magnet. Why does this occur?
The magnetic field aligns the magnetic domains mainly in one direction.
The magnetic field gives the ferromagnetic material an electric charge.
Long-range electric currents circulating in the iron make it magnetic.
The motion of the iron nuclei produces a magnetic field.
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multiple allele inheritance is traits controlled by more than 2 alleles (ex: pigeons having 3 alleles of one gene govern their feather color).

the skeletons of most mammals reach a certain size and then stop growing. however, many animals, including some mammals, keep growing throughout their lives. kangaroos, for example, just keep growing and growing until they die. also, the longer an animal lives the greater the chance it might catch some deadly disease.

causes

fossil fuels burn

cities become more industrialized

human population grows worldwide