The Shortest Sentence

What is the shortest (grammatically, semantically and syntactically) "proper" sentence in English ? I think it's "Be.", which is the same length as "Do." but comes before "Do." in alphabetical order of the initial letter. The sentence "I." lacks an object not to mention a verb, as do the exclamatories "O!", "Ah!", "Mm!", "La!" etc. So it would seem that "Be." is the winner, unless anyone can come up with another candidate?.