Noticing Sentences and Apostrophes

On the January 20, 2012 self-start no  answer based on the sentences is wrong.
However, whether you noticed or not, we will look at how apostrophes are used in the sentences.
You will receive another tape-in about ---

Stuff You Need to Know about Apostrophes

•    Apostrophes show two meanings.

•    An apostrophe s added to a singular noun shows possession.

•    An apostrophe after the s in a plural word shows possession.

•    Apostrophes also show where letters were removed.

•    Words shortened with apostrophes are called contractions.

Don’t let this confuse you:

•    Not every word that ends with an s needs an apostrophe.

•    Don’t rely on chance rather than meaning with the apostrophe

•    Don’t use apostrophes to show pronoun possession.

          his, hers, yours, its, theirs

 It's a matter of style whether you write  1800's or 1800s.

Ouch!  Can you find the error?