The Periodic Table of the Elements Does Not List Whole

Multiple Choice

The periodic table of the elements does not list whole numbers for atomic weights. Why?

A) The atomic weights are not predictable.
B) The atomic weights include protons and neutrons at 1 amu each, but they also include electrons, which weigh a lot less than one.
C) The atomic weight is the weighted average of the masses of the known isotopes of an element.
D) The atomic weights do not include isotopes.