sen X.
sen x.
sen I shall test this.
sen 'I shall test this.'
sen It worked!?
sen It worked?!
sen It worked!!
sen Some extra blanks are  here.
sen Some words. after the period
sen In this problem you are to write four methods.
sen In this problem you are to write four methods. Right!?
sen The sentence must end with a period, question mark, exclamation mark, or one of the two strings "!?" and "?!".
sen One. Two.
sen Xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.
sen Xxxxxxx xxxxxxxxxxxxxxx Xxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.