Answer:
All four words are the name of elements.
Hydrogen, oxygen, carbon, nitrogen, calcium, and iron are all important substances found in the body and in environments. They can be combined with each other, and with other substances to form larger compounds.
But i think the answer is nucleic acids..
Step-by-step explanation:
Well, hope it helps you..
I tried to answer it..
Your welcome in advance..
(◍•ᴗ•◍)