Weegy: A substance that is made up of only one kind of atom is an element. C. element. User: If an unknown substance CANNOT be broken down into simpler substances, it is
A. a compound.
B. an element.
C. made of one kind of atom.
D. both b and c Weegy: D. both b and c
User: If a material contains three elements joined in a fixed proportion, it is a(an)
D. compound. Weegy: D. compound. ... (More)