An example of a gas cooling and condensation taking place is when
A. ice cubes turn into water.
B. melted candle wax hardens.
c. water vapor in the air turns into water droplets on the outside of
a cold glass.
D. your shower water turns into steam.

it is b that is the answer.

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.