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

Action Reasoning:
Block c is currently held and block a is clear, which allows us to stack c on a, directly achieving the goal state.

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

Action Chosen:
stack(c, a)
