Which of the following best describes the difference between a mixture and a pure substance? A. A mixture has different properties throughout; a pure substance has the same properties throughout. B. A mixture is made up of more than one type of atom; a pure substance is made up of only one type of atom. C. A mixture is made up of only one type of atom; a pure substance is made up of more than one type of atom. D. A mixture has the same properties throughout; a pure substance has the different properties throughout.