No, there is no apostrophe in the phrase "21st century."
It was the third year of the 21st century.
1/21st.
December third 1818, it was the 21st state aded into the union
February 21st 2011, it falls on the third monday of February.
No, the first Avatar in 2009 was put out by 21st Century Fox. The second and third Avatars will also be by produced by 21st Century FOX however thanks to the acquisition of 21st Century FOX by Disney in December 2017 [finalized by Summer 2019], the third and fourth Avatars [assuming they are made] will in fact be Disney productions.
The latest the third Thursday of any month can be on is the 21st. Christmas is always on December 25th, so it can never be on the third Thursday.
Feb 21st to the 25th (third Monday of February)
it is being released on the 21st of december 2012
Being an Australian in the 21st century means accepting and adapting to the multicultural way of life
[Gemini] Gemini(♊) is the third astrological sign in the Zodiac.[ between May 21st to June 20th ]
Only if it's being used as an adjective.