There are 5 shapes on a 4x4 grid. Which shape is closest to the gray right_triangle in terms of Manhattan distance? The final answer is the grid position of the closest shape like (row_index, column_index).
<think>Target shape: gray right_triangle at (3, 1)
Distance from target shape to red square at (2, 1): 1
Distance from target shape to yellow trapezoid at (1, 1): 2
Distance from target shape to purple rectangle at (0, 2): 4
Distance from target shape to cyan square at (1, 3): 4
Closest shape is the red square at (2, 1) with distance 1</think>

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