Subtract the mass of the container Add leaves from other plants to the container Allow the leaves to settle in the container for a few days Use a metric ruler to measure the volume of the container
I gave my students this multiple choice question: Some students measure the mass of a small pile of leaves before and after the leaves decompose. Each time the students measure the mass, they place a container with the decomposing leaves on a balance. Before recording the mass of the leaves, the students must do which of the following?

Only one answer is correct among these 4 choices:
- Subtract the mass of the container
- Add leaves from other plants to the container
- Allow the leaves to settle in the container for a few days
- Use a metric ruler to measure the volume of the container

Could you tell me which one is correct?

Subtract the mass of the container