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 gave my students this multiple choice question: Why is it difficult to create a terrarium ecosystem that will last a long time without human help?

Only one answer is correct among these 4 choices:
- 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.

Could you tell me which one is correct?

Ecosystems with few species are weak and unstable.