The book is too expensive for me to buy.
改为同义句为
复杂句：The book is so expensive that i can't buy it。
或者
简单句：The book is not cheap enough for me to buy.
too + 形容词 + to do... 太...而不能...
He is too yound to join the army. 他因为太小而不能参军。
so + 形容词 + that + 从句 如此...以至于...
It's so hot that I couldn't sleep well. 天气如此之热以至于我不能睡得踏实。（天太热，我无法睡踏实）
