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(not a teacher)
Unofficially, I would say "By his looks" because as a native speaker, it just sounds correct. But for a more official explanation, cCheck WikiAnswers for the in-depth explanation of the difference between BY and FROM.
(not a teacher)
Unofficially, I would say "By his looks" because as a native speaker, it just sounds correct. But for a more official explanation, cCheck WikiAnswers for the in-depth explanation of the difference between BY and FROM.
By his look, Joshua assumed "boys" included Sarah and Hope as well.
Don't be fooled by his look. He's a terrific competitor.
She would have ruffled his hair, if she weren't warned by his look of seriousness.
He looked at me harder till I was persuaded by his look.
by/from 
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