Select the combination of letters that when filled in the blanks in the same sequence will make the series logically complete.
_GDIF_HMJO_QNSP_RWT_

Given: _GDIF_HMJO_QNSP_RWT_

Let's check options:

Option (a): CJMVZ

Sequence: C G D I F J H M J O M Q N S P V R W T Z   (Pattern Not Follow)​
​Option (b): BJLVY

Sequence: B G D I F J H M J O L Q N S P V R W T Y   (Pattern Not Follow)​​
​Option (c): CKMUZ

Sequence: C G D I F K H M J O M Q N S P U R W T Z   (Pattern Not Follow)​​
​Option (d): BKLUY

Sequence: B G D I F K H M J O L Q N S P U R W T Y   (Logical Pattern Follow)

Logic: The letters increase by +5 and decrease by -3 alternately.

B + 5 = G; G - 3 = D; D + 5 = I; I - 3 = F; F + 5 = K; K - 3 = H; H + 5 = M; M - 3 = J; J + 5 = O; O - 3 = L

L + 5 = Q; Q - 3 = N; N + 5 = S; S - 3 = P; P + 5 = U; U - 3 = R; R + 5 = W; W - 3 = T; T + 5 = Y

Thus, the correct option is (d) BKLUY.