Which of the following pairs of sets are not equivalent?

• A = {2, 4, 6, 8}, B = {u, v, w, x}
• A = {a, b, c}, B = {α, β, γ, δ, ν}
• A = {}, B = ϕ
• A = {x: x = 2n, n ∈ N}, B = {x: x = 2n + 1, n ∈ N}.