In an ecosystem, producers are organisms that can make their own food through photosynthesis or chemosynthesis. Green plants are considered producers because they use sunlight to produce food (glucose) through the process of photosynthesis.
- Option (A) Birds are consumers, not producers, as they feed on other organisms.
- Option (B) Wild animals are consumers, not producers.
- Option (C) Pet animals are also consumers as they depend on plants or other animals for food.
- Option (D) Green plants are producers because they produce their own food through photosynthesis.
Thus, the correct answer is (D) Green plants.