Grammar Notes

Data= plural
Datum= singular

Criteria= plural
Criterion= singular

Media= plural
Medium= singular

Multiple digits in a number= plural has no apostrophe. 1990s

For words that end in “ss”, add an “apostrophe s”.  Unless the next word begins with an “s”, in which case add an apostrophe without an “s”.

If a proper name ends in an “s”, add an apostrophe at the end for the possesive form.

Attorney general= singular
Attorneys general= plural
Attorney general’s= singular possessive
Attorneys general’s= plural possessive

For two different subjects (Bill and Marcy) with only one object (house) only put an “apostrophe s” after the last subject (Bill and Marcy’s).
For two different subjects (Bill and Marcy) with MULTIPLE objects (parents) put an “apostrophe s” after the both subjects (Bill’s and Marcy’s).

Citizens band radio or Scholars Academy are not possessive and therefore don’t bear the “apostrophe s”