Select the option that represents the letters that, when sequentially placed from left to right in the blanks below, will complete the letter series.
S O _ T _ S _ F _ Y _ O F T _ _ O F T Y

Let's count the total number of characters including blanks.
The template ends with "O F T Y". This strongly suggests a repeating pattern of 5 letters: S O F T Y.

Let's divide the series into blocks of 5 letters:

S O _ T _ → should be S O F T Y (Blanks: F, Y)

S _ F _ Y → should be S O F T Y (Blanks: O, T)

_ O F T _ → should be S O F T Y (Blanks: S, Y)

_ O F T Y → should be S O F T Y (Blank: S)

Let's list the letters filled in the blanks sequentially from left to right:
F, Y, O, T, S, Y, S

Thus, the required sequence is FYOTSYS.