An Element's Mass Number Tells Us Which of the Following

Multiple Choice

An element's mass number tells us which of the following?

A) The number of protons in an atom of that element.
B) The number of protons + electrons in an atom of that element.
C) The number of electrons in an atom of that element.
D) The number of protons + neutrons in an atom of that element.
E) The number of neutrons in an atom of that element.