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envelope:
n. 信封,封皮包膜[天] 包层包迹
Don't forget to put a stamp on the envelope.
不要忘记在信封上贴邮票。
letter:
n. 信字母,文字证书文学,学问字面意义
vt. 写字母于
vi. 写印刷体字母
Business letters should be written in clear and logical language.
商业信函的语言应当清楚且有逻辑。
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