This book is cheap enough for him to buy it.为什么要去掉it

问题描述:

This book is cheap enough for him to buy it.为什么要去掉it

the book已经作buy的逻辑宾语,有It就重复了

this book 就是buy 的逻辑宾语

因为这里的it和前面的this book重复了.
sth is cheap enough for sb to buy.固定词组,对某人而言,某件东西足够便宜,他有能力去买(有买东西的钱)
后面不需要再加it了.