Select the one substance that is not a rock.

 - Wool is made by living things. It is a solid.
 - Chalk is a solid. It is not made by living things.
 - Soapstone is formed in nature. It is not made by living things.
Compare the properties of each substance to the properties of rocks. Select the substance whose properties do not match those of rocks.
Wool is made by living things. But rocks are not made by living things.
So, wool is not a rock.
Chalk is a rock.
Soapstone is a rock.