it is only because they konw what they are for that thay are working with such admirable zeal.
问题描述：
it is only because they konw what they are for that thay are working with such admirable zeal.
句子意思没有问题,语法上分析不出来
it是形式主语,实际的主语是哪部分only because they konw what they are for
that 是表语从句的开头,用主系表表达了because they konw what they are for ,thay are working with such admirable zeal.
以上分析有问题吗,为什么要用主系表+形式主语的形式
答
It is.that.是强调句.把it's 和that去掉,句子的意思不改变,可以读通.it引导的强调句型,通常形式为：It＋be＋被强调部分＋that／who＋其它.这种强调句由普通陈述句转换而来,用来强调句子的主语、宾语或状语.例如： ...