Nack
abbr. 否定应答（Negative Acknowledgement）
🗣️ 情景例句
you had some doubts about wanting to go to Michigan.
你对上Michigan大学有些疑虑。
On a crowded train, one comes in contact with many people.
在拥挤的火车里面，会和许多人接触。
That's terrible.
真糟糕！