Attempt Number: 2
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 where Block C is on top of Block B, we first need to clear Block C. The best action is to unstack Block B from Block C, which will make Block C clear and allow us to stack Block C on Block B later.

New State Description:
Block c is on the table and clear. Block b is in the hand and no longer on Block c. Block a is on the table and clear. Block d is on the table and clear. The hand is holding Block b.

Action Chosen:
unstack(b, c)
