Nitrate reduction test.
Three organisms (B, C, and D) were tested for nitrate reductase.
•Tube A is shown before addition of reagents.
•Tubes C and D are shown after the addition of zinc dust.

Which organism:
•Produces nitrate reductase?
•Reduces NO₃^-- to NO₂^-?
•Reduces NO₃^- to N₂?

Use the key below to help you interpret the results.