4 to duoc phan cong lam ve sinh san truong neu chi co to mot, hai, ba cung lam thi sau 2 phut se xong. neu chi co to hai, ba , bon cung lam thi sau 15 phut se lam xong. neu chi co to mot , bon cung lam thi sau 20 phut se xong.hoi neu 4 to cung lam thi sau bao lau se xong