想问一句英语句子的结构

题目

想问一句英语句子的结构
Today an estimated 160,000 people speak Yiddish at home in the U.S.,half the number who did in 1980.不用翻译,整句话意思我也懂,就是想知道这後面half the number who did in 1980算是一个什麽从句?为什麽不用half the number of people who did in 1980,再如果直接用half the number of who did in 1980行不行呢?

答案