DO you think he will be happier?该如何回答?应该说“Yes,I do”还是“Yes,he

你是对的
Do开头提问的句子,
如果是一般疑问句,回答时就用“Yes, 主语+Do（肯定）或No, 主语+don't(否定), ”
如果是选择疑问句,回答是按实际情况.
如:
Do you think it right?
Yes, I do.
No, I don't.
Do you go to school by bike or by bus?
I go to school by bus.
I go to school by bike.
Neither. I go to school on foot.