请问 as if与as though ,even if与even though,so far as 与 as long

as though 是书面语比as if正式,意思上没有区别； even though 和even if 同理.
so/as far as;as/so long as 如果是用于表示“只要”时,用法上没有区别.只是它们各自还有各自的用法：so/as far as I know据我所知；A is as long as B.A和B一样长.