the rate of……谓语的单复数取决于the后面的名词，该名词是单数或不可数的，则谓语动词单数；该名词是复数，则谓语动词是复数

例句：

Now we look at the rate of change in the volume of hell .现在，我们计算下地狱里的交换率。

She churns out novels at the rate of three a year .她以一年三本的速度粗制滥造地写小说