Which of these is true about pure substances? A. They may contain one type of atom or one type of molecule.
B. They can contain different types of atoms and molecules.
C. They can only contain one type of molecule.
D. They can only contain one type of atom.

B. They can contain different types of atoms and molecules.

Explanation:

A pure substance only has one type of particle that can either be atoms, molecules, elements, or compounds.

answer : a model is often used to explain and make things easier to understand when any scientific topic needs to be demonstrated and explained.

as in this case where a scientist wants to use a model to present the results of his detailed scientific investigation. he should do it as it will him to make the audience understand the concept in a much better way. also, it can be changed according to new scientific understandings.

58750.08068 is the answer i think