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 c on block a. First, we need to clear block c by unstacking block d, which is currently on top of it.

New State Description:
Block d is now held in the hand, block c is clear and on the table, block a is on block b, and the hand is not empty.

Action Chosen:
unstack(d, c)
