根据句意及首字母提示完成句子。

1. We can't get good grades w       your help.

2. Let's sing the song t         .

3. Mary is the q          girl in her class.  

She speaks little.

4. Last week's talent show w        a great success.

5. Harbin is in n         China. It's very cold.

根据工程对象的不同，土木工程又可分为哪几大类？