I believe that forms that are added to the letters are not relevant to sample detection.
The letters can be replaced by numbers in two ways (A = 1, B = 2, C = 3, D = 4) 2 4 2 4 4 2 3 1 2 2 1 3 3 3 4 4 or (A = 4, B = 3, C = 2, D = 1) 3 1 3 1 1 3 2 4 3 3 4 2 2 2 1 1 irrespective of how the letters are replaced by numbers, the sum of the two rows from the top and bottom are equal, such as the same are sums of the two columns on the right and on the left.
The letters can be replaced by numbers in two ways (A = 1, B = 2, C = 3, D = 4)
2 4 2 4
4 2 3 1
2 2 1 3
3 3 4 4
or (A = 4, B = 3, C = 2, D = 1)
3 1 3 1
1 3 2 4
3 3 4 2
2 2 1 1
irrespective of how the letters are replaced by numbers, the sum of the two rows from the top and bottom are equal, such as the same are sums of the two columns on the right and on the left.
So the answer:
number 4 is correct (A missing)