is+副词的用法：例句it is (likely等副词) you would finish the task!

is+副词的用法：例句it is (likely等副词) you would finish the task!
还有个例句：it is precisely (恰恰,准确的) because of the war that science can------.
都是it is+副词
一、我记得it is+形容词+that.但好多句子都是it is+副词,这个是什么用法?
二、还有个问题就是：
it is+形容词+that 这里的that能省略吗?
it is+副词,这里的that到底能不能加?我看it is +副词的句子一般没有that,想问问
求教达人,