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。
