根据句子意思，用括号中所给单词的适当形式填空。
The （关键） to success is to learn from mistakes and never give up．
Erquan Yingyue is one of the most moving pieces of music that I （hear）．
Nowadays sky lanterns （see） as bright symbols of good luck．
Tom went to basketball practice with （勇气） rather than fear in his heart．
This morning the traffic was （crowd） so I was not late for work．