Answer:
Because they don't have fertilizer.
Explanation:
Well, if this was a long time ago, then farmers did not have fertilizer. So, there are bacteria on the roots of plants that convert nitrogen into a usable form. It's very important for growing, and when farmers harvest the crop, not much of the nitrogen is returned to the land, so it is not as fertile. Fertilizer is largely consisted of nitrogen, so that is why farmers use fertilizers today. But "a long time ago," farmers did not have fertilizer.
The answer would be : a. angiosperms.
Source : https://en.wikipedia.org/wiki/Flowering_plant
Hope this helps !
Photon
The energy needed by a system to initiate a process is called as the activation energy. It describes the minimum energy which must be available to a chemical system with potential reactants to result in a chemical reaction. Hope this answers the question.
Answer:
D
Explanation:
Most of the energy in the United States comes from the burning of fossil fuels (coal, oil, natural gas). Hope this helps!
