It may be faith. So it faith is in your word bank then that's probably it, and if faith isn't in the word bank, then I will need to know the words that are in the word bank.
The answer is C
Why:
A - this is natural
B - water is natural
D - this is also natural
C- this is right because when we breathe out we produce more carbon dioxide then we breathed in.
The brick is solid because it's not hollow or containing spaces or gaps
