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.