a. It’s a one hundred and twenty year-old building.
b. It’s a a hundred and twenty year-old building.
c. It’s a hundred and twenty year-old building.
d. It’s one hundred and twenty year-old building.
I have another question for you. These questions you ask with multiple choice answers - are they made by you personally or are they part of an exercise you are doing?
Thank you for your very full and honest answer. It was good to hear your reasons and to learn some more about you. Please don’t think that your questions are silly. Any question is worth asking and we do our best to give an answer. I certainly would appreciate it if, as you say, you’ll give some background on your questions so that in context we can give you a more satisfactory answer. And another point is that the other users online can get some idea of the nature of the question