cantus planus

例句：

1. 1. The music was so beautiful that it could be heard from afar.
   音乐如此美妙，以至于可以从远处听到。
2. 2. The cantus planus is the foundation of the orchestra.
   主奏乐器是管弦乐队的基础。
3. 3. The cantus planus is played by the principal conductor.
   主奏乐器由首席指挥演奏。