While it's easy to do if you're trying to make a point or explain something, try not to touch other people's screens and definitely don't touch any screen if you've got dirty fingers.
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3. 他们的手经常很脏，穿的工作服也不干净。
They usually have dirty hands and wear dirty work clothes.
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4. 我的手是不干净，你又能拿我怎样？
My hands aren't clean. So what?
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5. 不要拿干净的手碰其他人用不干净的手触摸过的地方，这是不卫生的。
It is not sanitary to touch areas with clean hands that others have touched with dirty hands.
