一根吸管可以从b里面吸出牛奶

Ning Cheng didn't say anything. Xu Yingdie definitely said that Yin Kongchan wasn't the one who did it, but her tone pointed at Yin Kongchan. The only thing that can't be explained is why Yin Kongchan didn't kill the two of them in the end. Unless there really is a fourth person, but if there is a fourth person, it cannot be justified....