Answer: C. X17O
procedure:
1.how X came
add 2 letters to previous one;
P + 2 = R; R + 2 = T; T + 2 = V; V + 2 = X
2.how 17 came
add 2,3,4,5... for the number
3 + 2 = 5; 5 + 3 = 8; 8 + 4 = 12; 12 + 5 = 17
3.how O came
add 3 letters to previous one
C + 3 = F; F + 3 = I; I + 3 = L; L + 3 = O