Answer: 4
Step-by-step explanation:
Fungi(mushrooms) are heterotrophs and they cannot fix nitrogen from the atmosphere and they must obtain it from their environment. They are using complex organic compounds as a source of carbon.
Most plants can fix carbon which are 1. Grass 2. Maple trees 3. Algae and hat are why they are incorrect answers because from this question only 4. mushrooms can fix carbon.