Note: each letters are assigned a unique value according to the question.

Option (A): $b=4,d=2$, it satisfies only condition (ii), same value $(4)$ for different letters (b,d). so it is wrong.

Option (B): $a=4,e=6$, put these values on (I) we get $c=2$,on (iii) we get $b=10$, using $b$ value we get $d=5$

Option (C): $b=6,e=2$, put this values on (iii) we get $a=4$,in (I) we get $c=2$. here we get the same value for the different letters (c,e) so it is wrong.

Option (D): $a=4,c=6$, put this values on (I) we get $e=10$,on (iii) we get $b=14$, from $(ii)$ we get $d=7$. since the value $7$ is not given in question so it is also wrong.