AB
Here, A is the 10th digit = 10A, B is the single digit = B, Therefore, 10A + B
BA
Here, B is the 10th place = 10B, A is the single digit = A, Therefore, 10B + A
Therefore, 11A + 11B = (A+B)*11, meaning A+B >=10. That means, A+B = 11
CDC
Here, both the value of C should be same. since A and B is 2-digit number, they can make up to 3 digit number.
To find CDC, lets check which number can come.
101, 111,
121, 131, 141, 151, 161, 171, 181, 191
Only 121 is divisible by 11. Others are not.
Therefore, C = 1 and D = 2
A+B = 11 can be
1+ 10 = 11 (Cannot possible as C = 1)
2+9 = 11 (Cannot possible as D = 2)
3+8 = 11
4+7 = 11
5+6 = 11
Therefore, 3 separate ways we can sort out A, B, C, D.
Answer: 3 (B)