Sffd
abbr. step-function frequency discriminator 阶跃函数鉴频器
🗣️ 情景例句
(looking at his calendar) Oh, next Friday is May 4th.
（正在看着日历）哦，下周五是五月四号了。
A creaking door hangs long on its hinges.
户枢不蠹。
Where are you travelling to, Gary?
卡里，你打算旅行到哪里呢？