用适当的介词或副词填空。

1. At the party, we congratulated him ________ his success.

2. In the letter, she expressed her thanks ________ her teacher _______ his help.

3. The little boy wanted his parents to be proud ________ him, so he studied very hard.

4. Judging ________ his clothes, he is a student.

5. The meeting will begin ________ 8 o'clock ________ September 1.

大型变压器的主保护有（）。

A、瓦斯保护；

B、差动保护；

C、瓦斯和差动保护；

D、差动和过流保护。