the color of the sample the mass of the sample the amount of clay in the sample the amount of rock in the sample
I gave my students this multiple choice question: Humus is an organic material that makes up soil. Which characteristic best indicates that soil has a high humus content?

Only one answer is correct among these 4 choices:
- the color of the sample
- the mass of the sample
- the amount of clay in the sample
- the amount of rock in the sample

Could you tell me which one is correct?

the color of the sample