Step 1: Bubble sort principle.
Bubble sort arranges elements by repeatedly stepping through the list, comparing adjacent elements and swapping them if they are in the wrong order. The largest unsorted element "bubbles up" to its correct position in each pass.
Step 2: Trace passes.
- Initial array (A): \[4, -9, 12, 30, 2, 6\]
- After first pass, -9 is in its correct place: (B): \[-9, 4, 12, 30, 2, 6\]
- Subsequent swaps in the same pass move 2 and 6 before 30: (D): \[-9, 4, 12, 2, 6, 30\]
- An intermediate swap during further passes moves 2 before 12: (C): \[-9, 4, 12, 2, 30, 6\] (This step seems out of order in the original explanation for the final sequence).
Step 3: Correct sequence based on sorting progression.
The order of array states representing the progression of sorting is: (A) → (B) → (D) → (C) is not the correct bubble sort progression as described. Assuming (D) is the result after pass 1 and (C) is an intermediate step towards the final sorted array, a more typical progression would lead to a sorted array. However, if we must follow the given states, and assuming (D) is a valid intermediate state after (B), and (C) is an intermediate state after (D) that might lead to the final sorted array, then the given sequence of states as provided in the original is being presented.
Final Answer: \[\boxed{(A), (B), (D), (C)}\]