zài / diàn / zǐ / yóu / jiàn / pǔ / jí / yǐ / qián / rén / men / cháng / yòng / háng / kōng / yóu / jiǎn / gěi / hǎi / wài / qīn / yǒu / xiě / xìn

在电子邮件普及以前，人们常用航空邮简给海外亲友写信。

Before email became widespread, people often used aerograms to write to friends and relatives overseas.