How are cyanobacteria related to the atmosphere?
A. It is believed they were the first
oxygen-producing organisms.
B. They live in the upper troposphere
of the atmosphere.
C. They are believed to produce
carbon dioxide into the
atmosphere.
D. They fed off the abundant
nitrogen in the atmosphere

There would have to be three nitrogen atoms in the products. The law of conservation of matter states that the amount of substance before a reaction occurs  should be the same as the amount of substance after the reaction.

Explanation: This is the EXACT sample answer from the test, just reword it if you want. ^