It was along the Mississippi River_____(that/where)Mark Twain spent much of his childhood.选填并分析句子成分告诉我为什么

选择that it was ……that句型是强调句。把这三个英文单词从句中删除，再读句子，句意完整，语法正确就是强调句。。。

where,这是个定语从句，而从句Mark Twain spent much of his childhood.
中不缺宾语或主语，所以不能用which，而从句中刚好缺地点状语，而where引导的是地点状语

选that ,强调句型
正常的语序是：
Mark Twain spent much of his childhood along the Mississippi River.
马克吐温 大部分童年时光 都是在密西西比河沿岸度过的
主语 谓语宾语 状语
现在为了强调状语,即密西西比河沿岸,将状语提前,强调句型格式是：
it is/was +强调部分 that 句子其他部分

It was along the Mississippi River_____(that/where)Mark Twain spent much of his childhood.
along the Mississippi 是强调部分，是个地点状语，用where