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> Can sentence 1 mean either "The letter was sent by the teacher" or "The letter was sent to the teacher"?
It can only mean "The letter was sent to the teacher". To express "The letter was sent by the teacher", a direct translation would be , but this is extremely awkward; it is way more natural to say
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> Can sentence 2 mean "I was unfortunately sent a letter by my teacher" or "A letter was sent to the teacher and it indirectly impacted me"?
It can only mean "I was unfortunately sent a letter by my teacher". To express "A letter was sent to the teacher and it indirectly impacted me", it would be ()