It is years of hard work___has made him what he is today.这里填that,为什么不能填which?

It is years of hard work___has made him what he is today.这里填that,为什么不能填which? It took years of hard work to speak good English(把years of hard work换成hard work of year不行么?) it is years of hard work that has made him what he is today.求大神详细分析这个句子的主干. it is hard to think of a world without you i know that it will take years of hard work to become a doctor是什么意思 it is too hard It is hard to 英语翻译句子：John's success has nothing to do with good luck .It is years of hard work that has made him what he is today.It was more than a pesonal experience.词组：has nothing to domore than it is natural enough after long years of childhood. 英语翻译Private-owned Small and Medium-sized enterprises in China contribute considerably to Chinese economy these years.It is hard to ignore the growing significance of SMEs in China's economy.But,there are some serious problems emerge during it It is a kind of fruit.Touch it.It is rough and hard.Smell it.It is smelly.It is not nice.What is it? John's success has nothing to do with good luck.It is years of hard work ______has made him what he is today.A.why B.when C.which D.that John’success has nothing to do with good luck,it is years of hard work（ ）has made him what heis today A why B when Cwhich D that tend to be...有上下文I have a flip phone,and it's so old all the paint is worn off of it.I think I've had it for 6 or 7 years now.That's doing good for me,I tend to be really hard on phones 最后一句i tend to be really hard on phones 要如何 It is raining ____(hard). It is hard to wait It is hard to please It is hard to select!