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

Action Reasoning:
The next best action is to stack `d` onto `b` as it aligns with the goal state's requirement of `d` being on `b` and doesn't violate any constraints in the current state.

New State Description:
Block `a` is on the table and clear. Block `b` is on the table and supporting block `d`. Block `c` is on the table and clear. Block `d` is on block `b` and clear. The hand is empty.

Action Chosen:
stack(d, b)
