What does being an "elementary substance" mean? Which of the following isn't an elementary substance?

Ozone
Sulfur
diamond
quartz


I don't get what elementary substance means.
By seeing the options and the word elementary, I guess it means something like pure or obtained in its original form.
From LATINTOS:


  An elementary substance is a pure chemical substance that consists of atoms belonging to a single chemical element. 


Now you should be able to solve your question.