Concept:The series follows a repeated operation pattern; the odd term breaks it.Explanation:Start with 21.Multiply by 3: 21×3=63.Subtract 3: 63−3=60.But the series has 69 instead of 60.Check further: 60×3=180.Then 180−3=177.So the pattern is ×3,−3,×3,−3.Thus, 69 is the wrong term.Answer:The odd term is 69, i.e. option D.