Attempt Number: 3
Error Message: Action not unique compared to other actions chosen from this state before. Choose a new action

Action Reasoning:
In the current state, block `c` is blocking access to block `a`. We should first move block `a` from on top of block `c` to make progress toward the goal state, where block `a` will eventually be placed on block `d`. To move block `a`, let's put-down `block_c`, which indirectly helps make the stack of `a` on `d` achievable after final `unstacking a` on hand.

New State Description:
Block `d` is on the table and clear. The hand is holding block `a`. Block `a` is no longer on block `c` and no longer clear but being held. Block `c` is now clear and on top of block `b`. Block `b` is on the table. The hand is not empty as it holds block `a`.

Action Chosen:
unstack(a, c)
