Assuming you have everything imported that is needed to use Bootstrap, create a responsive structure using the grid system as described below.

1. The template should span the entire width of the screen.
2. There should be three columns. The left and right columns should each take up 25% the width of the screen when the viewport is anything larger than small. The middle column should take up the remaining 50% of the screen.
3. Inside the middle column there should be two more columns, the left column taking up 75% of the width of it's parent and the right column taking up the remaining 25% when the viewport is anything larger than small.
4. All columns should stack vertically and respond when the viewport is small.