Answer:
Change in the species structure of an ecological community over time. (A)
Explanation: Google
There is only one main element involved in the fusion reactions inside the sun; Hydrogen, but if you need a second element then it is more than likely that the question is asking for the isotope of hydrogen that is called <span>deuterium.
So basically, Hydrogen and Deuterium; an isotope of hydrogen</span>
It is a cold Artic air mass over Siberia. Air masses are altered because it doesn't stay in one place and changes as it moves due to the temperature of environment that can be caused by moisture. The cold Artic Mass from Siberia will go to the North Pole, Canada then moves further to the South area.
