http://grammar.ccc.commnet.edu/grammar/marks/period.htm http://grammar.ccc.commnet.edu/grammar/marks/period.htm This is a prob. I tested! This is a problem

http://grammar.ccc.commnet.edu/grammar/marks/period.htm http://grammar.ccc.commnet.edu/grammar/marks/period.htm This is a prob. I tested! This is a problem I tested! This is a prob.  I tested! This is a problem. I tested!