a note of sadness的用法和样例：
- D'Artagnan could not help detecting a note of sadness in his voice.
- I will make a note of that man's name.
- She sounded a note of warning in her speech.
- I thought I even detected a note of sadness in his tone. We were quiet for a long time. My peevishness had vanished. I thought of my father.
- Make a note of how much money you spend.