一道英语选择题，选哪个，为什么？多谢。

Question

The speed ______ light travels is said to be the maximum in the universe.
A. in which B. by which C. from which D.at which

Answer 1

选d at the speed 是固定搭配表示以.....的速度 the speed(at which light travels)is said to be the maximum in the universe 括号内的是定语从句 我们可以造个句 the light travels at the speed of 3000000000 meters per second 这样你就明白了吧。

Answer 2

d吧，这是个定语从句，speed是先行词，light travelS at the speed，用which代表speed，就应该是at which

Answer 3

B. by which

by有通过某种方式/形式的意思.

常见by sea ,by road ,by air, by car,

这里by the speed of .... 也是同理。