Answer:
C. The mass is used for growth, stored, or excreted
as waste. The energy is stored, used in cellular
respiration, and lost to the environment as heat.
Explanation:
I got it right on the quiz.
The mass number is the sum of the number of protons and number of neutrons the atom has.
So, we can write the equation as:
x + 20 = 40
x = 20 neutrons.