The picture shows part of the trademark of a certain drinking natural water. The physical and chemical indicators are listed in the picture. Based on this, answer questions 1-2 (2009? Gaochun County model) Calcium and magnesium here

A. The mass of the atom is too small and difficult to operate, so it is not the content of the atom, so A is wrong.

B. The mass of the molecule is also very small and difficult to operate, so B is wrong.

C. The proton has a very small mass in the atom. It is difficult to measure its mass in practice, so C is wrong.

D. Elements are macroscopic concepts that can be measured using instruments, so D is correct.

So choose D.