were single-celled. had organ systems. were multi-cellular. had small appendages.
I gave my students this multiple choice question: Fossil records indicate that Earth was first inhabited by bacteria-like organisms. These organisms

Only one answer is correct among these 4 choices:
- were single-celled.
- had organ systems.
- were multi-cellular.
- had small appendages.

Could you tell me which one is correct?

were single-celled.