I think doing something for your parents is the best gift.此处为啥填do 的ing形式呀?

题目

I think doing something for your parents is the best gift.此处为啥填do 的ing形式呀?

答案

doing something for your parents 做名词,放在系动词is的前面,而
do something for your parents 是动词,不能放在系动词is的前面.
doing something for your parents is the best gift
名词 系动词 名词
明白没?
PS 这个与I think没有关系,是个宾语从句,后面可以随意+个句子
句子意思就是
我认为为你的礼物做点事情就是最好的礼物.