Select the option that represents the letters that, when sequentially placed from left to right in the blanks, will complete the letter series.R AR_O _GOA_GO

Let's count the total number of characters including blanks.The series contains 15 slots: _ R _ _ A R _ O _ _ G O A _ G O (Wait, let's count characters precisely from text: _R_ _AR_O_ _GOA_GO $\to$ 1. _, 2. R, 3. _, 4. _, 5. A, 6. R, 7. _, 8. O, 9. _, 10. _, 11. G, 12. O, 13. A, 14. _, 15. G, 16. O). Let's look for a repeating pattern.Notice the substring patterns ending with GO and containing AR:Let's check if the word is CARGO or ARGO. Since there is 'R' and 'O' and 'G', 'O', let's test a repeating block pattern of 5 letters: A R G O _ or similar.Let's try a 5-letter repeating sequence: A R G O AFirst block: A R G O A (Blanks filled: A, G, O)Second block: R G O A R $\to$ doesn't match cleanly.Let's look at Option B (AGOGARR):Substituting option B into the blanks sequentially:1st blank: A $\to$ AR2nd blank: G $\to$ ARG3rd blank: O $\to$ ARGO4th blank: G $\to$ ARGOA5th blank: A $\to$ ARGOAR6th blank: R $\to$ ARGOARO $\to$ Wait, let's align it index by index:The prompt string: _ R _ _ A R _ O _ _ G O A _ G OLet's test Option B: A, G, O, G, A, R, RA $\to$ ARG $\to$ ARGO $\to$ ARGOG $\to$ ARGOA RG OA $\to$ ARGOA RGOAR $\to$ ARGOA RGOAR G O AR $\to$ ARGOA RGOAR G O AR G OLet's look at the completed string:A R G O A | R G O A R | G O A R G | O...This is a shifting cyclic pattern of the 5 letters: A, R, G, O, A (or rather, the letters shift positions progressively).First 5 letters: A R G O ANext 5 letters: R G O A R (shifted by 1 position left)Next 5 letters: G O A R G (shifted by another position left)Next letters: O...This perfectly completes the series. The letters filled in are AGOGARR.