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受動態:be動詞+動詞の過去分詞 です。
1. [Our college was founded in] 1913. ※受動態:was founded
2. [The flight may be canceled] because of the snow. ※受動態:may(助動詞) be canceled
3. [The password should be changed] once in a while. ※受動態:should(助動詞) be changed
4. [The comic-book-character has been loved for] more than forty years. ※受動態:(has) been loved 現在完了受動態
参考にしてください。