Which of the following six decays are allowed in lowest-order weak interactions?

(a) K⁺ → π⁺ + π⁺ + e⁻ + ν̅_e, 

(b) K⁻ → π⁺ + π⁻ + e⁻ + ν̅_e, 

(c) Ξ⁰ → Σ⁻ + e⁺ + ν_e, 

(d) Ω⁻ → Ξ⁰ + e⁻ + v̅_e, 

(e) Ξ⁰ → p + π⁻ + π⁰, 

(f) Ω⁻ → Ξ⁻ + π⁺ + π⁻.