回答
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①If you are expecting that all the teachers are professional, that is a big mistake.
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②If you are expecting that all the teachers act professionally, that is a big mistake.
①は、all the teachers are professional=資格を持っている、ようにイメージできる
②は、all the teachers act professionally=資格所有という意味ではなく、プロ意識をもって。。。というイメージ
ピンキリ。。。(^^;同感です。