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 'a' on block 'c'. First, pick up block 'a' since it is clear and on the table.

New State Description:
The hand is holding block a. Block c is on the table and clear. Block b is on the table with block d on top of it. Block d is on block b and is clear. Block a is no longer on the table and is not clear.

Action Chosen:
pick-up(a)
