to后不一定都是加動詞原形的.
你給的句子He was very happy to_______,這里要用原形,be happy to do sth.
如果to作為介詞,而不是短語中的固定搭配,后面一般跟的是名詞或者人稱代詞
,比如:
He went to the supermarket last night.
Please pick up the book and give it to me.
某些固定搭配還可以跟動名詞,比如look forward to sth./doing sth.
We are looking forward to your next visit.
I am looking forward to going shopping with you.
你說的加第三人稱單數(shù)的情況好像是沒有的.不會因為句子的助于是he,后面就填第三人稱單數(shù),句中的系動詞was已經起了這個功能.