Attempt Number: 2
Error Message: Action not unique compared to other actions chosen from this state before. Choose a new action

Action Reasoning:
To progress towards the goal state, the next logical step is to remove block `c` from block `b` so that block `b` becomes clear. This allows `d` to be stacked on `b` in subsequent steps.

New State Description:
Block `a` is on the table and clear. Block `b` is on the table and clear. Block `c` is in the hand and not clear. Block `d` is on the table and clear. The hand is holding block `c`.

Action Chosen:
unstack(c, b)
