这个是动词不定时的用法,当前有to后面的就不加to,例如：I like to eat bananas and play baseball有些要加，如Constant practice has such as effect on memory as to lead to skillful performance on the piano,to recitation of a poem,and even to reading and understanding these words.这个为什么要加呢?这个是说的是哪个toand even to你看这个to后面加的是do么，是to doing 这就说明这不是动词定式，不要混了明白了么