Answer:
nuclear fusion
Explanation:
When the density and temperature at the core of the gravitationally collapsing nebula reaches values when nuclear fusion is triggered and sustained, that marks the birth of the star.
Answer:
I don't understand you you now that I'm super girl
Polar air masses are characterized by cold air near the surface while tropical air masses are warm or hot.
Yes an organ can belong to more than one system because the organ system is the digestive system.