Which drawing (a) to (d) shows this stack of cubes as it looks from the front?

Look along each line from front to back and take the tallest column. First line: 0, 1, 2, tallest 2. Second: 2, 3, 1, tallest 3. Third: 3, 1, 0, tallest 3. Fourth: 1, 0, 0, tallest 1. So 2, 3, 3, 1: (b). (a) shows only the front row; (c) is the view from the back.