What Is Meant by the Term "Positive-Inside Rule

What is meant by the term "positive-inside rule"?

A) The typical transmembrane potential for plasma membranes is positive on the inside.
B) Integral plasma membrane proteins commonly have positively charge amino acids on the cytosolic side.
C) Concentrations of cations are usually higher inside than outside of cells.
D) All of the answers are correct.
E) None of the answers is correct.