Scientists study salamanders and their ability to regenerate lost legs and tails. What additional information is essential for scientists to understand in order to apply this ability to humans who have lost limbs? how quickly the body parts regenerate
how similar salamanders are to humans
which body parts are most often lost
which genes control regeneration

The answer could be:

(/) which genes control regeneration

(/) how similar salamanders are to humans

(x) how quickly the body parts regenerate  (salamanders' size and form does not equate to human beings)

(x) which body parts are most often lost  (it was already given that it's legs and limbs)

it’s lava came from an explosive eruption

the relative atomic mass of an element is the mass of one atom of that element, relative to 1/12th of the mass of a  1212c atom. to convert to an absolute mass in kg, it is necessary to multiply by  1.661×10−271.661×10−27.

the relative atomic mass is roughly equal to the number of neutrons, plus the number of protons, in the nucleus of the atom.

for elements with more than one stable isotope (different types of nucleus with different numbers of neutrons but the same number of protons), the quoted mass is usually the average mass, weighted by the relative abundance of the different isotopes.