postal course的用法和樣例：
例句
- He is following a correspondence course in gardening for adults with comparative ease.
他正在上一個相對簡單的園藝成人函授課程。 - A correspondence course is offered by mail, completed entirely by home study, often with one or two proctored, or supervised examinations.
函授課程是透過函件往返，學生完全是在家以自修方式完成，通常會有一或二次經由學校監督進行的考試。
