for people still think of it as a day for giving thanks.补充原句：Thanksgiving Day is also a day for students to give thanks to parents and teachers,for people still think of it as a day for giving thanks.think前怎么不加to,for后面怎么

for people still think of it as a day for giving thanks.补充原句：Thanksgiving Day is also a day for students to give thanks to parents and teachers,for people still think of it as a day for giving thanks.think前怎么不加to,for后面怎么
for people still think of it as a day for giving thanks.补充
原句：Thanksgiving Day is also a day for students to give thanks to parents and teachers,for people still think of it as a day for giving thanks.
think前怎么不加to,for后面怎么用doing形式?
请整体分析一下句型结构吧.

for people still think of it as a day for giving thanks.补充原句：Thanksgiving Day is also a day for students to give thanks to parents and teachers,for people still think of it as a day for giving thanks.think前怎么不加to,for后面怎么
for people still think of it中的for本就带有对..来说的意味,加to的话语义上就不太通顺.as是作为的意思吧.后面的for表示目的.是介词,自然要加ing形式~

for people still think of it as a day for giving thanks
这句的意思是:因为人们仍然认为那是一个用来感恩的日子!是一般的叙述现状,当然不用不定式;
as在这里的意思是"作为,当作"的意思;
for是个介词,后面当然要用动名词形式!

think of ... as ...是一个固定搭配，表示”认为。。。是“”把。。。看作/当成“。
think of ... as ＝look on ...as =have...as
for 是介词 后面接动词当然要用动词的ing形式哦。因为只有名词和代词才可以做介词宾语。这里giving做动名词。