In a bowl, combine flour, baking powder, salt and baking soda; cut in margarine until crumbly. Combine yogurt and sugar; stir into the dry ingredients just until moistened. Turn onto a floured surface; knead 4-5 times. Place on a baking sheet that has been coated with non-stick cooking spray; pat into a 6-inch X 4-inch rectangle. Cut into 6 square biscuits (do not seperate biscuits). Brush tops with milk. Bake at 450° for 12-15 minutes or until golden. Serve warm.