Which answer most correctly describes the Balantidium coli stages shown in the diagram below?

(a) 1=Trophozoite; 2=oocyst; 3=infective cyst 
(b) 1=Trophozoite; 2=mature cyst; 3=oocyst 
(c) 1=Trophozoite; 2=mature cyst; 3=immature cyst
(d) 1=Trophozoite; 2=immature cyst; 3=infective cyst