1. Apostrophes Use with Contractions they’re class of ’14 it’s
Use an ’s to form the plural of a word discussed or a letter. (Not needed for numbers, symbols, and dates)
There are two perhaps’s in that sentence.
The word occurrence is spelled with two r’s.

2. Apostrophes the 60s the 1800s Possessives:
No apostrophe is needed centuries and decades
the 60s the 1800s
Possessives:
Singular Nouns (exceptions: Jesus’/Moses’)
’ + s = possessive Dr. Fisher’s
Plural Nouns (that end in s)
’= possessive classes’ calendars
Compound Nouns
’ + s = possessive mother-in-law’s

3. Apostrophes Joint possession:
Use ’s on the last noun if the two share possession.
mom and dad’s room
Use ’s after both if the two have separate possession.
Bush’s and Clinton’s presidencies