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

Action Reasoning:
The best next action is to pick up block 'b' since it is clear and on the table, allowing us to then stack it on block 'a' to move closer to the goal state.

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

Action Chosen:
pick-up(b)
