As a result , the CDS is such a useful instrument for hedge funds and the trading desks of investment banks that it seems inconceivable it will go away.

于是，CDS成了对冲基金和投资银行交易部门非常有用的投资工具，根本无法想象没有CDS的情形会是如何。

They had invented a calendar which proved such a useful instrument for the purpose of measuring time that it has survived with a few changes until today.

他们发明的日历能精确地计量时间，稍加修改后，一直沿用至今。

Teachers need a theory in the reflection of their practice. The mathematical tasks framework can act as a useful instrument and guide for teachers to reflect on their own instruction.

教师在进行教学反思时需要一种理论，数学任务框架是教师进行教学反思的有用工具或指南。