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

Action Reasoning:
The goal is to have block `b` on top of block `c` with block `c` on the table. Since block `c` is currently on block `b`, I will unstack `c` from `b` to move `c` to the table, bringing us closer to the goal.

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

Action Chosen:
unstack(c b)
