In the correctly-worked addition operation above, A, B, C, and D each

Answer is D.

A. D = 2B => this cannot be true when value of B is equal to or greater than 5.

B. B > 5 => B can be less than 5 also, since unique digit can range from 0 to 9 without any conditions.

C. C = 2A => this cannot be true, when value of B is equal to or greater than 5. Let's say if B=5, A =4, then C=4+4+1=9, which conflicts the statement.

D. A < 5 => This condition must be true because if A is equal to or greater than 5, then it will have value equal to or above 10, but the given statement is -> C is a unique digit, so value of C can be maximum 9.

E. D > B => This statement cannot be true when value of B is equal to or greater than 5. eg. If B=5, then D=0, which conflicts the given statement.