Select the letter that when placed in the blank of the given series will complete the series.

MNO, PQR, STU, V___X

Given: MNO, PQR, STU, V___X

Logic: Each letter is increasing by + 3 in alphabetical order.

First letters: M → P → S → V
M + 3 = P
P + 3 = S
S + 3 = V

Second letters: N → Q → T → ?
N + 3 = Q
Q + 3 = T
T + 3 = W

Third letters: O → R → U → X
O + 3 = R
R + 3 = U
U + 3 = X

So, the missing letter is W
The complete group is: VWX

Thus, the correct option is (c) VWX.