Parent State ID: 18
State Depth: 5
Action Taken: pick-up(block_d)
Action Reasoning: To align with the goal state, we will first move block D onto block C. Since the hand is empty and block D is clear, the best next action is to pick up block D.
State Description: Block A is on the table and clear. Block B is on block C and clear. Block C is on the table and not clear. Block D is in the hand and not clear. The hand is holding block D, which is not on the table or on any block.
Action Path: ['unstack(block_b, block_c)', 'stack(block_b, block_d)', 'unstack(block_b, block_d)', 'stack(block_b, block_c)', 'pick-up(block_d)']

INACTIVE REASON: action path invalid: The last action, pick-up(block_d), is invalid because the preconditions are not met: block_d is not clear, and the hand is not empty. The current state's natural language description and visualization are accurate, but the action sequence is incorrect.
