Correct option is B
Given:
B_KPBN_R_OKTB_KVBQK_
From the options (b)

First and third letter B and K are constant.
second letter - M -N - O - P - Q
Fourth letter - P -- R -- T -- V -- X
second letter - M -N - O - P - Q
Fourth letter - P -- R -- T -- V -- X
Thus, the correct answer is (b) MKBPX.