Only once: During the time I was in Paris, I saw only once

Dear teachers,

Please choose the correct sentences:

  1. During the time I was in Paris, I only once saw the River Seine.
  2. During the time I was in Paris, I once only saw the River Seine.
    3.During the time I was in Paris, I only saw the River Seine once.
    4.During the time I was in Paris, I saw once only the River Seine.
    5.During the time I was in Paris, I saw only once the River Seine.

What is the rule?
Thanks
Quoc

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The rule is: put the adverbs in their most common positions unless you wish to draw attention to them or to the enclosing utterance for some reason. To me, the usual position for only once in your sentences is #3; #s 1 and 5 are second choices. The remainder seem odd to me.
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