Answer:
A. green algae
Explanation:
A: Green algae, or algae, are single-celled organisms. Because they go through photosynthesis, just like any other plant-like organism, they're a producer.
B: Mushrooms are fungi, and all fungi are decomposers. Therefore, mushrooms are decomposers.
C: Fungi and bacteria are the most common decomposers, so bacteria is clearly a decomposer.
D: Earthworms eat dead/dying organic matter in the ground, so they're decomposers.
Therefore, the answer is A. green algae.
