standard musical pitch

例句：

1. 1. The standardfor measuring the length of a ruler is20 cm.
   测量尺子长度的标准是20厘米。
2. 2. Thestandard operating procedure for thistask is to follow the instructionsstep by step.
   完成这项任务的标准操作程序是按照步骤一步步进行。
3. 3. Thestandard for excellence in this field is high.
   这个领域的卓越标准很高。