There are 6 shapes on a 4x4 grid. Which shape is closest to the red rectangle in terms of Manhattan distance? The final answer is the grid position of the closest shape like (row_index, column_index).
<think>Target shape: red rectangle at (1, 1)
Distance from target shape to gray rectangle at (2, 2): 2
Distance from target shape to purple right_triangle at (2, 1): 1
Distance from target shape to yellow right_triangle at (0, 1): 1
Distance from target shape to brown trapezoid at (3, 1): 2
Distance from target shape to green trapezoid at (1, 0): 1
Closest shape is the purple right_triangle at (2, 1) with distance 1</think>

<answer>(2, 1)</answer>