The symbol ca-40 denotes that

a. a calcium atom contains 40 protons
b. a calcium atom contains 40 electrons
c. a calcium atom contains 40 neutrons
d. a calcium atom has a mass number of 40

elements make up everything, and they combine to make compounds.

the answer is c

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.