A square requires that adjacent sides be equal.

So the problem is to find the least common multiple of 12 and 9 (find 36).

Later, I learned that the length of 12 needs to be overlapped by 3 rows and the width of 9 needs to be overlapped by 4 columns.

Total 3X4= 12.

So d is correct.

Besides, there are other ways to solve this problem.

For example, 12X9= 108.

Divide 108 into factors.

108=3X6？ ,

Therefore, multiples of 108 are all square numbers, all less than 36X36, and only18x18 =108x3. However, 18X 18 cannot be spelled with rectangles of 9 and 12. So it can only be 36X36= 108X 12, so it is 12 ~