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[化] 反馈作用
🧩 词语组成解析
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[bæk]
n. 背，背部;背面，反面;后面，后部;（椅子等的）靠背;
vt. 使后退;支持;加背书于;下赌注于;
vi. 后退;倒退;
adj. 背部的;后面的;以前的;拖欠的;
adv. 以前;向后地;
🗣️ 情景例句
Have you ever done supervisory work?
你担任过管理工作吗？
While there is life, there is hope.
留着青山在，不怕没柴烧。
He's been there for over two years. He's been there since two years ago.
他到校有两年多时间了。他两年前就到那儿学习了。