D. It was an exceptional unit of length.

D. 这是一个特殊的长度单位。

In the UK, the yard was considered the base unit of length.

在英国，码被认为是基本的长度单位。

36. According to the text, what was the basic unit of length in the UK?

36. 根据本文，英国的基本长度单位是什么？

A light-year is a unit of length, with one light-year equaling the distance that light would travel in a vacuum in one year.

一光年是长度单位，一 光年等于光 在真空中一年的传播距离。