The BEST example of a primary source is

Aan article about the Battle of the Alamo by a history professor.
Ba Wikipedia article about the Texas Revolution.
Cthe diary of the commanding officer's aide.
Da website run by Texas Revolution reenactors.

Verified Answer :

Cthe diary of the commanding officer because the source is from when the event occurred whereas the other sources are after the fact.  

I believe that the best example of a primary source would be C 
I hope that helps at least a little :)