In order to convert carbon in plants into carbon in animals, animals need to use digestive enzymes. So process 2 would use digestive enzymes.
Same principle applies to process 3. Decomposers digest carbon in animals. So process 3 uses digestive enzymes.
During respiration, carbon in decomposers is converted to carbon dioxide in air. So 4 uses respiratory enzymes.
In order to convert carbon dioxide in air to carbon in plants, plants use photosynthesises. This neither involves digestive enzymes nor respiratory enzymes. So 1 should not be in either of those columns.
Column 1 (digestive enzymes) = 2 and 3
Column 2 (respiratory enzymes) = 4 only
The answer is H