在下面句子的空白处填入一个最适当的词，使句子意思完整，语法正确。

Tim, come on! We must find ________ who broke the window.

在下面句子的空白处填入一个最适当的词，使句子意思完整，语法正确。

The door is ________, but nobody is in the room.

在下面句子的空白处填入一个最适当的词，使句子意思完整，语法正确。

It's polite to ________ at the door before you enter the teachers' office.

在下面句子的空白处填入一个最适当的词，使句子意思完整，语法正确。

－Hello, Xiaogang! In which season can you see lots of snow in the northeast of China?

－In ________.

完成下列句子的反意疑问句。

The boy can hardly answer this question, ________?

用所给词的适当形式填空

Could you tell me where tea is ________?(grow)

用适当的介词或副词填空

—What’s the sweater made ________?

—Wool, I think.

用适当的介词或副词填空

My watch is made ________ Sweden.

用适当的介词或副词填空

The work is too hard, so I can’t do it ________ myself.

用适当的介词或副词填空

Stamps are used ________ sending letters．