Select the option that is related to the first letter cluster in the same way as the fourth letter cluster is related to the third letter cluster and sixth letter cluster is related to fifth letter cluster.
SEP : ? :: WKJ : BPO :: IQV : NVA

Given: SEP : ? :: WKJ : BPO :: IQV : NVA

Logic: Letters are increasing + 5 place.

For, WKJ : BPO

W + 5 = B, K + 5 = P, J + 5 = O

For, IQV : NVA

I + 5 = N, Q + 5 = V, V + 5 = A

Similarly,

SEP : ?

S + 5 = X, E + 5 = J, P + 5 = U

So, SEP : XJU

Thus, correct option is (b).