In the given sequence, the position of O is increasing from the back to the front of each post. XXXOXO ⇒ O placed in 4‌th and 6‌th position. XXOXOX ⇒ O placed in 3‌rd and 5‌th position. XOXOXX ⇒ O placed in 2‌nd and 4‌th position. OXOXXX ⇒ O placed in 1‌st and 3‌rd position. That is the correct answer.