Subtyping
v. 子类型化（subtype的现在分词）
🗣️ 情景例句
Hi, Marilyn.
嗨 Marilyn。
I didn't know whether to send the letter airmail or not.
我不知道是否送航空邮件。
He showed that the average individual's sleep cycle is punctuated with peculiar bursts of eye-movements,
他指出，平常人的睡眠周期中不时伴有一阵阵奇怪的眼球队活动，