根据句意和汉语注释,写出单词的正确形式。
Although you failed the exam, you can learn a ________ (宝贵的) lesson from it.
The man kept remembering English words every day until he was in his _______ (九十).
This is one of the most famous __________(大学) in the USA.
He is the ______(严格) teacher I have ever met. But I like him a lot.