我怎样才能得到三个列，同胞div，每个扩展以填充其父级？

I have been searching forever. Sorry, I am pretty desperate at this point so I thought I would ask here. Below is an HTML sample. When column B is longer than a single page (viewport, sorry I am not sure on the correct terminology here) then A and C are not expanding in height to fill the container div. They fill the entire page but stop at a single page length even if column B is longer than a single page. Any ideas, i have been pulling my hair out. I have been playing around with height and min-height and nothing seems to work.I have been searching forever. Sorry, I am pret