this is why in the early days of radio.有错误吗？怎么改？

This is because in the earlydays of radio,those who reported the news were expected to speak excellent English.

这是因为在广播的早期，那些报道新闻的人被要求说一口流利的英语。

句子分析：

主句主语是this，

系动词是is,

表语是because引导的表语从句,

in the early days是时间状语,

of radio作定语修饰前面名词days.because引导表语从句,

主语是those,

系动词是were,to speak excellent English是表语.定语从句