Answer to Question 1
Hydrogen.
Answer to Question 2
Once the usable hydrogen fuel is all burned up, there remains a helium-rich core. Once fusion is finished in the star's core, there is insufficient pressure to prevent collapse due to gravity, and the contraction generates a huge increase in internal temperature, triggering a higher level of hydrogen fusion in the star's shell. The outer shell expands from the heat of accelerated fusion, but this expansion simultaneously cools the star's surface, yielding a large, cool star.
Structure of cellulose, the main macromolecule of the primary cell wall
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World Total Energy Consumption by Fuel Type
The five skills of the element Analysis of Situation
The lacO region O1 containing an inverted repeat sequence