Yes: X.
No: x.
Yes: I shall test this.
No: 'I shall test this.'
Yes: It worked!?
Yes: It worked?!
No: It worked!!
No: Some extra blanks are  here.
No: Some words. after the period
Yes: In this problem you are to write four methods.
No: In this problem you are to write four methods. Right!?
No: The sentence must end with a period, question mark, exclamation mark, or one of the two strings "!?" and "?!".
No: One. Two.
Yes: Xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.
Yes: Xxxxxxx xxxxxxxxxxxxxxx Xxxxxxxxxxxxxxxxxxx xxxxxxxxxxxxx xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx.