吉他手弹奏了一个C大调和弦，听起来很和谐。

The guitarist played a C major ___chord that sounded very harmonious.

老师用粉笔在黑板上画出了连接圆上两点的弦。

The teacher drew the ___chord connecting two points on the circle with chalk.

那首老歌触动了他的心弦。

The old song struck a ___chord in his heart.