Answer:
D. a pure substance that is made up of different elements
Step-by-step explanation:
Step-by-step explanation:
There are two types of pure substances: elements and compounds.
Elements are made up of only one type of atom. And compounds are pure substances, that are made up of more than one type of element. Like - magnesium oxide. It is a compound of a metal with a non-metal and is held together with ionic bonds.