Certs
n. 确实的事情（cert 复数）
🗣️ 情景例句
You've really been keeping an eye on quality.
你们的确在质量上下了功夫!
Why are you so sad?
你为什么这样伤心？
Once the oxygen content of the air had risen to 25% it was ready to burn.
一旦氧气在空气中的含量达到25%，它就要燃烧。