16.I know nothing about her except 　　she is from Canada.

解析：that引导的宾语从句作介词except的宾语。

答案：that

15.We know little about the young lady except 　　 you told me.

解析：此为what引导的宾语从句，作介词except的宾语，而在从句中what作told的宾语。

答案：what

14.The fire destroyed 　　 was in the building.

解析：whatever(一切东西)引导宾语从句，作动词destroy的宾语。whatever相当于anything that。

答案：what/whatever

13.There's a feeling in me 　　 we'll never know what a UFO is.

解析：此为that引导的同位语从句，应在抽象名词feeling后，起补充说明的作用。

答案：that

12.　　 he doesn't like them is very clear.

解析：此为that引导的主语从句。这个句子也可以改成用it作形式主语的句子：It is very clear that he doesn't like them。

答案：That

11.I have no idea 　　 heavy the box is.

解析：此为how引导的同位语从句，在抽象名词idea后起补充说明作用。

答案：how

9.Now we can see 　　a serious problem the population is.

解析：从see一词可判断从句为宾语从句。

答案：what

you tell me 　　 there's a post office near here？

解析：此为if或whether引导的宾语从句。if/whether是否。

答案：if/whether

8.You have no idea 　　 anxious I have been for her safety.

解析：此处how引导的从句表示抽象名词idea的具体内容，是同位语从句。

答案：how

7.It depends on 　　 we have enough time.

解析：此为whether引导的宾语从句，作介词on的宾语。

答案：whether

6.The suggestion 　　 students should learn some practical knowledge is worth considering.

解析：此为that引导的同位语从句，在抽象名词suggestion之后，起补充说明的作用。注意该句要用虚拟语气。

答案：that