You see a boat sitting at the end of a dock. Ten minutes later you see the same boat in a cove to the right of the dock You did not see the boat move. However, you know that the boat moved because its
relative to the dock changed.

No action is required. The sailboat should change course and speed.

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.