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by rule按惯例，墨守成规地，刻板块；by degrees逐渐地；by accident偶然，意外地；by request应邀；by good (ill) luck侥幸地（不巧）；by mistake弄错；by force用武力；by heart熟记。
如：He does everything by rule.（他总是按照惯例行事。）We can only make progress by degrees.（我们只能循序渐进。）He had a slip of tongue by accident.（他偶然说漏了嘴。）She sang a song by request of the Queen.（她应女王的要求演唱了一首歌。）By ill luck, my flight had been cancelled.（不巧的是，我乘坐的班次被取消了。）The burglar alarm was activated by mistake.（防盗铃误响了。）take power by force（武装夺取权力）；learn large numbers of phrases by heart（背诵大量词组）。
