What is a pure substance that contains only one kind of particle?

I thought it was pure substance. But i recently took a Science Test of these subject(i'm also in 8th grade) and it was the same question...EXACTLY! I put down Pure substance as well but appearantly the answer was "All of the Above" which included A.Pure Substance B.Compound C.Element ... so as long as you can prove it was only pure substance( This was for extra credit to get points back on the test for my teacher) You got the points. In my opinion a Pure Substance is the substance in which there is only one type of particle. I hoped this helped :)