Attempt Number: 4
Error Message: Action not unique compared to other actions chosen from this state before. Choose a new action

Action Reasoning:
To achieve the goal state, I need to clear each block from the top down. Since block 'b' is clear and can be directly removed, the next best action is to pick up block 'b' from block 'c'.

New State Description:
The hand is holding block 'b'. Block 'c' is clear. Block 'd' is on top of block 'a'. Block 'a' is on the table. Block 'b' is no longer on block 'c' and is not clear as it is in the hand.

Action Chosen:
unstack(b, c)
