- An algae is a kind of organism
- Algae is found in bodies of water
- A body of water is a kind of marine ecosystem
- Hence, algae is an organism found in marine ecosystems

- Algae is usually green in color
- Algae is a kind of plant
- So, algae is a kind of green plant

- Algae is a kind of green plant
- Green plants are a kind of producer
- Therefore, algae is a kind of producer

- Algae is an organism found in marine ecosystems
- Algae is a kind of producer
- So, algae is a kind of producer found in marine ecosystems

Therefore, algae is a kind of producer found in marine ecosystems
Q: Which of these organisms is a producer in a marine ecosystem?
Context:
- An algae is a kind of organism 
- Green plants are a kind of producer 
- Algae is usually green in color 
- Algae is found in bodies of water 
- Algae is a kind of plant 
- A body of water is a kind of marine ecosystem