L1: Apostrophe for Possession: Use an apostrophe to indicate possession. Be sure to apostrophe in the proper place based on whether the noun is singular or plural. See Writing for Success Section 3.5 p.118 or the following: http://grammar.ccc.commnet.edu/grammar/possessives.htm
Use an apostrophe to indicate that a noun is possessive.
Roy’s dog managed to climb out on the driver’s side.
If the noun is singular and ends in “s,” add an apostrophe and an “s.”
Lois’s sister spent last year in India.
If the noun is plural and ends in “s,” add only an apostrophe.
Both diplomats’ briefcases were stolen.
For joint possession, use an apostrophe and “s” after the second noun.
Have you seen Joyce and Greg’s new car?