由于這個(gè)句子實(shí)際上的主語（if/ whether 引導(dǎo)的主語從句）太長(zhǎng),而用it作為句子的形式主語,make是句子的謂語
It makes no difference whether he will attend the meeting or not.他是否會(huì)參加會(huì)議都無關(guān)緊要.
It makes no difference if he doesn't know me.
他知不知道我并沒什么區(qū)別.
it構(gòu)成的主語從句
（1）由連詞that引導(dǎo)的主語從句,在大多數(shù)情況下會(huì)放到句子的后面,而用代詞it作形式主語.如：
It is well-known that the earth moves around the sun.眾所周知,地球圍繞太陽轉(zhuǎn).
需要注意的是,it作形式主語代替主語從句時(shí),要注意和as引導(dǎo)的定語從句的區(qū)別.試比較：
It was reported that the US was under the terrorist attack.（主語從句,有that,無逗號(hào)）
As was reported,the US was under the terrorist attack.（定語從句,無that,有逗號(hào)）上兩句意為“據(jù)報(bào)道,美國(guó)遭到恐怖分子的襲擊”.
（2）常見用it作形式主語的復(fù)合句結(jié)構(gòu)
It is a fact （a good idea / a pity / a shame / no wonder / good news…）that…如：
It's a pity that you missed the film.你沒有看那部電影真是太遺憾了.
It is necessary （clear / true / strange/ important /wonderful / possible / likely…）that…
需要注意的是,這類主語從句中,謂語動(dòng)詞很多為“（should）＋動(dòng)詞原形”,即要用虛擬語氣.如：
It is necessary that you （should）master the computer.你很有必要掌握電腦.
It is important that a student learn English well.學(xué)生學(xué)好英語很重要.
It's clear that they badly need help.很明顯,他們急需援助.
It is likely that a hurricane will arrive soon.颶風(fēng)很可能馬上就要到達(dá)了.
It is reported （well-known / hoped / thought / expected /said /believed/decided /suggested /ordered…）that…如：
It is said that he was killed in the earthquake.據(jù)說他在地震中喪生了.
It seems （happened / appears / doesn't matter / makes no difference / …）that …如：
It seems that they will win the game.看起來他們好像會(huì)贏得這場(chǎng)比賽.
It makes no difference whether he will attend the meeting or not.他是否會(huì)參加會(huì)議都無關(guān)緊要.