重点4 what和that引导的名词性从句
what在英语中非常活跃,它可以用来引导主语从句、宾语从句、表语从句，但是不用来引导定语从句。在句子里可以充当主语、宾语、表语、定语，既可以指人，也可以指物。
例句：
What is the population of the world?
That he’ll achieve his dream is certain.=It is certain that he’ll achieve his dream.
What is most important in life isn’t money.
Will you show me what you bought?
Mary is no longer what she was ten years ago.。
what we need is time.
