If it is possible to make only one such number with the first, the forth and the sixth digits of the number 531697 which is the perfect square of a two-digit even number, which of the following will be the second digit of the two-digit even number. If no such number can be made, give '@' as the answer and if more than one such number can be made, give '©' as the answer
1) 4
2) 2
3) 6
4) @
5) ©

Options

A. `4k,4k+1`
B. `4k+1,4k+3`
C. `4k+2,4k+3`
D. `4k,4k+2`