题目内容：

China is not the country (that) it was ,that为什么做表语?

优质解答

这个that是定语从句中"was"的表语.即country为先行词,而that充当关系代词,指代"the country".
分成2个句子比较好理解一些,China is not the country.China was the country.合成一起,就成了你给的句子的定语从句.显然,that,即代指country,是was的表语