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, we need to stack block 'b' on block 'c'. Both blocks 'b' and 'c' are currently clear and on the table, so the best action is to pick up block 'b'.

New State Description:
Block 'b' is held in the hand. Block 'c' remains clear and on the table. Block 'a' is on top of block 'd', which is supporting block 'a'. The hand is no longer empty.

Action Chosen:
pick-up(b)
