Which one of the following languages over Σ = {a, b} is NOT context-free?

• A. {wwR |w ϵ {a, b}*}
• B. {wanbnwR |w ϵ {a, b}*, n ≥ 0}
• C. {wanwRbn|w ϵ {a, b}*, n ≥ 0}
• D. {anbi |i ϵ {n, 3n, 5n}, n ≥ 0}