An apostrophe is also used to form some plurals, especially
the plural of letters, symbols, and digits.
Regina received four A's on her report card.
Timothy used too many &'s in his paper.
The judges gave the diver two 9's and two 8's.
It is no longer considered necessary or even correct to create
the plural of years or decades or abbreviations with an apostrophe.
He wrote several novels during the 1930s.
There are fifteen PhDs on our faculty.
My sister and I have identical IQs.
(If you wrote Ph.D. with periods, you would add an apostrophe
before the pluralizing "s": Ph.D.'s) If the abbreviation
ends in "S," it's a good idea to separate this final
"S" from the pluralizing "s" with an apostrophe: