The answer would be terms. The terms are being separated by addition as well as the subtraction signs. They are parts of the algebraic expression that contains numbers as well as operations and one or more symbols.Hope this would help.
Easy. Answer is oxygen because it says which one was missing before any life was on earth. And in order to have life on earth you need oxygen!
:)
Answer:
Nitrogen fixing bacteria in the soil and within root nodules of some plants convert nitrogen gas on the atmosphere to ammonia.
Nitrifying- bacteria convert ammonia to nitrites.
