Acooling curve has two flat lines, or plateaus. what does the plateau at the higher temperature represent?

condensation

Explanation: because of condensation is when gas becomes liquid, and is the higher plateaus in the cooling curve

the answer is 1 i believe

answer is: nuclear fusion produces elements that are heavier than helium.

nuclei combine to form a heavier nucleus, releasing energy.  

for example, fusion of hydrogen atoms at the sun.  

this fusion nuclear reaction is in the inner core of the sun and hydrogen (atomic number 1) is conveted into helium (atomic number 2).  

the inner core is the central region of the sun and all solar energy is produced in the core by nuclear fusion.