at which 是引导定语从句吗

If the only reading you ever do is the novel or magazine, thespeed at which you read probablydoes not matter very much. But if you have to read a great deal for study, youwill appreciate the benefits of being able to read more quickly. Here are sometips to help improve your reading speed. 

这是2021年新高考考试英语全国卷2的阅读理解七选五中的一段。请问句中的 at which 是引导定语从句吗？感觉结构有点奇怪。

没错，at which you read 是定语从句，修饰 thespeed。意思是“你阅读的速度”。这里用介词 at，是由于 speed 一般搭配 at（表示“以……速度”）。又如：

The police measured thespeed at which the car was travelling. 警察测定那辆汽车行驶的速度。

It was the speed at which itall happened that shocked me. 令我感到震撼的是整个事情发生得这样之快。

The driver miscalculated thespeed at which the other car was travelling. 司机对另一辆车的车速估计错误。