These statements are about a gas. 1. It is produced by thermal decomposition of a carbonate.
2. It is produced by the fermentation of glucose.
3. It makes up 1% of unpolluted air.
4. It is produced during the production of steel from iron.

Which statements are correct for carbon dioxide?
a. 1 and 2 only
b. 1, 2 and 3
c. 1, 2 and 4
d. 1, 3 and 4
e. Other