Estimating the expansion rate of the universe is a notoriously difficult problem because there is no single yardstick by which all distances can be measured 。OG上的一道题的正确答案,想问问各位这个" by which "当中的by 怎么理解呀?为什么必须有呢? 我看答案也没看懂。
句子大意如下:
估计宇宙的膨胀率是一个众所周知的难题,因为没有一个单一的尺度,通过这个单一的尺度,可以衡量所有的距离。
by是通过的意思,by which合起来就是通过这种方式的意思
还原最后的从句就是:
all distances can be measured by a single yardstick