How do you reply to "How are you?" ? When someone says "How are you?"　to me, I always reply with the same phrase, "I'm fine, thank you." I don't know the expression except "I'm fine." How do you say for "I'm fine." and "I'm not fine." ?

When do you say going down questions? When I was a student, I learned English grammar from Japanese at school. 　My teachers said, "In these cases, the questions that can answer with yes or no, you should say going up the ending of them. On the contrary, the questions starting with interrogative, you should say going down the ending of them. However, I hear you say going up even with interrogative. What is correct? When do you say going down questions? どんな質問のときに語尾を下げて言いますか？

The house the roof of which we can see from here was built one hundred years ago. Is this sentence on the textbook I am studying now grammatically correct ? I think it's necessary to insert something between " The house" and "the roof". Please tell me if it's correct or not, and please explain it in grammar.