根据下列句子及所给汉语注释,写出空缺处各单词的正确形式,每空只写一词。
A lot of boys want to be ________(士兵) after they leave school.
What _________(造成) the dog’s death is still a secret.
The lake became much _________(深) after a heavy rain.
Have you heard of the _________(古老的) Chinese legend before?
It seems that he is always full of ________(活力).