a geometric pattern formed by a mineral a solid element or compound from Earth's crust remains of an extinct organism found in a rock layer bits of weathered rocks and pieces of dead organisms
I gave my students this multiple choice question: Which of these best describes a fossil?

Only one answer is correct among these 4 choices:
- a geometric pattern formed by a mineral
- a solid element or compound from Earth's crust
- remains of an extinct organism found in a rock layer
- bits of weathered rocks and pieces of dead organisms

Could you tell me which one is correct?

remains of an extinct organism found in a rock layer