Concavities
n. 凹面, 成凹形( concavity的名词复数 )
🗣️ 情景例句
These are polite questions.
这些问题都是礼貌的。
After forty years teaching English he thinks it's time to call it a day.
他教英语四十年，认为该退休了。
but Captain Fawcett did not take him because the trip was too dangerous.
弗西特机长之所以不送他去，是因为那段飞行太危险了。