a dour warning的用法和样例：
- He did, in fact, become a dour ascetic.
他, 实际上, 成为一个阴郁的禁欲主义者。
- The game proved to be a dour struggle, with both men determined to win.
- He was a silent, precise man with a dour nature and a hard Aberdonian accent.
- A dour, self-sacrificing life.
- The teacher let him off the hook with a warning this time.