at

1. The picture looks better at a distance.（指距离）

2. He succeeded at the third attempt.（指顺序）

3. The two counties are at war.（指状态）

4. The students marvelled at the extent of her knowledge.（表原因）

5. They were delighted at the idea of going to England.（表原因）

6. We buy articles at ￥30 and sell them at ￥35.（指价格）

7. The train was running at full speed.（指速度）

8. We did the work at his request.（依照）