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).

中国的民歌依靠（）获得语音的平衡。

A.遣词造句

B.改变发音

C.衬词

D.升降调结合