Design six icons for a survey

I write surveys, and need six black and white line-drawing icons to indicate:
Agree strongly
Agree
Neither agree nor disagree
Disagree
Disagree strongly
Don't know

For agree and disagree, I'd like a smiley face icon and a sad face icon, the neutral one can just have a straight mouth, but not sure about the other three - they need to have obvious meaning to people in any language or of any reading ability.

I'd like the files delivered as jpegs. They are to be printed at a size of less than 1cm square each (probably just half that), so need to be incredibly clear even when reproduced very small.

This is a really simple job - the 'agree' only needs to be a circle with two dots and a smiley mouth!