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。
小题1: A lot of boys want to be ________(士兵) after they leave school.
小题2:What _________(造成) the dog’s death is still a secret.
小题3: The lake became much _________(深) after a heavy rain.
小题4: Have you heard of the _________(古老的) Chinese legend before?
小题5:It seems that he is always full of ________(活力).