Ihave asked this before, to get more points, just put the same answer on the other questions
describe how atomic masses are determined for the periodic table.

The standard atomic weight is the average mass of an element in atomic mass units. Though individual atoms always have an integer number of atomic mass units, the atomic mass on the periodic table is stated as a decimal number because it is an average of the various isotopes of an element.

i think the answer is d. good luck.