分析句子语法成分It might have been,but it didn’t have to be going that fast in order to appear to be separated from the sound.

Why Is It So Difficult To Spot A Plane In The Air?
How many times have you heard a jet plane going over, looked up to see it, but not been able to find it even though you were looking toward where the sound was coming from? Well, this moment of science is going to tell you why you couldn't find it?
Sometime during your life you might have been told that the plane wasn’t with the sound because it was traveling faster than the speed of sound. It might have been, but it didn’t have to be going that fast in order to appear to be separated from the sound.
句子分析：这是一个由but并列两个分句的并例句，为避免重复，两个句子共用了一个分词短语going that fast ...（第一个句子省略了）
分句1：主it +助动词be的情态完成式might have been+(going that fast ....)
分句2：主it +助动词be的半情态否定式 didn’t have to be+( going that fast ...)
共同的谓语动词go的现在分词
其同的方式状语that fast
共同目的状语：in order to appear to be separated from the sound.
译：它（指飞机）为了显得与声音分开【不同步地传到人的眼睛（形）和耳朵（声音）】可能飞得比声音快，但它不必飞得那么快。

to appear to be separated from the sound 主句
It 代指 to appear to be separated from the sound
要点：
that 这里与so一样，只是表示“那么”的意思，不表示从句结构
大意：
为了能使其从声音中分离出来，也许需要那么快，但也没有十分必要。

it 主语 might 情态动词 have been going 谓语but 连词 连接It might have been和it didn’t have to be that fast 状语修饰going 为了好理解 你可以看成这样It might have been going that fast,but it didn’t hav...