whether与if 均为"是否"的意思。但在下列情况下，whether 不能被if 取代：
1. whether引导主语从句并在句首
2. 引导表语从句
3. whether从句作介词宾语
4. 从句后有"or not"
Whether he will come is not clear.
家政服务培训大部分连接词引导的主语从句都可以置于句末，用it充当形式主语。
It is not important who will go.奶粉与牛奶
电脑怎么下载It is still unknown which team will win the match.
二. 主语从句
1. 作句子主语的从句叫主语从句。主语从句通常由从属连词that，whether，if和连接代词what，who，
which，whatever，whoever以及连接副词how，when，where，why等词引导。that在句中无词义，只起连接作用；连接代词和连接副词在句中既保留自己的疑问含义、又起连接作用，在从句中充当从句的成分。例如：
What he wants to tell us is not clear. 他要跟我们说什么，还不清楚。
Who will win the match is still unknown. 谁能赢得这场比赛还不得而知。
It is known to us how he became a writer. 我们都知道他是如何成为一名作家的。
Where the English evening will be held has not yet been announced. 英语晚会将在哪里举行，还没有宣布。
2. 有时为避免句子头重脚轻，常用形式主语it代替主语从句作形式主语放于句首，而把主语从句置于句末。主语从句后的谓语动词一般用单数形式。常用句型如下：
（1）It + be + 名词+ that从句
（2）It + be + 形容词+ that从句
花瓣儿鱼读后感（3）It + be + 动词的过去分词+ that从句
whether是什么意思
It is believed that 25 years after construction, the building was dismantled and moved timber by timber to the South Bank of the Thames, where a reconstruction of the theatre now stands.
据信经过25年的建设后，该建筑物将被拆处.并且该建筑物的一砖一石将被移到泰唔士河的南岸.重建的戏剧院现在正座落于此。
It is thought the cost of this lost labour is around £1 billion (10 billion yuan) to businesses and the economy.
大家一直认为这次对贸易和经济失去劳动力的损失的费用应该在10亿英镑（人民币100亿元）
It is not known how many of the 59 million words Mr Shea has remembered but he has certainly made history with his eccentric hobby.ds3水准仪