What is the shortest complete sentence in English?

There are two main candidates for the shortest sentence in the English language:

'Go!'
'I am'.

Why 'Go!'?

My vote is for 'Go!' because it has:

an active verb
an implied subject
a clear meaning.

I am only has meaning when used as an answer to a question: Who is going to the Moon this morning? I am. In any case, two words beats three!

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