Terrarium ecosystems cannot get enough sunlight. Terrarium ecosystems cannot get enough oxygen. Ecosystems with few species are weak and unstable. All ecosystems require thoughtful human management.
I am hesitating between 4 options to answer the following question, which option should I choose?
Question: Why is it difficult to create a terrarium ecosystem that will last a long time without human help?
Possibilities:
- Terrarium ecosystems cannot get enough sunlight.
- Terrarium ecosystems cannot get enough oxygen.
- Ecosystems with few species are weak and unstable.
- All ecosystems require thoughtful human management.

Ecosystems with few species are weak and unstable.