In such type of questions, clues are given regarding comparisons among a set of persons or things with respect to one or more qualities. The candidate is required to analyse the whole information, form a proper ascending / descending sequence and then answer the given questions accordingly.

A is elder to B while C and D are elder to E who lies between A and C.
If C be elder to B, Which one of the following statements is necessarily true ? 

A. A is elder to C
B. C is elder to D
C. D is elder to C
D. E is elder to B
Answer: D . E is elder to B


In terms of age, we have :
B < A,  E < C,  E < D,  B < C.
Since E lies between A and C, the sequence becomes :
B < A < E < C < D  or  B < A < E < D < C.
Clearly, whichever may be the case, E is elder to B.
Hence, (d) is necessarily true.