Does anyone know the answer to Xiao Liu's question? Please, thank you.

The first question, Xiao Ming and his girlfriend go for a walk by the river. When his girlfriend fell into the water, he went down to save him. He fished for a long time and found nothing. He went home crying. Two years later, he revisited his hometown and saw two old people chatting by the river. One said: clear water means no fish. There are no aquatic plants in this river, so there are no fish. Hearing this, Xiao Ming lost his mind on the spot and drowned himself. Excuse me, why is this? Mother and daughter, mother died and two sisters attended the funeral. My sister saw a handsome man at the funeral and liked it very much. A month later, my sister murdered my sister. Why? Xiaoming lives in a small house on the top of the mountain. He heard someone knocking at the door in the middle of the night. When he looked at the door, he fell asleep again. After a while, someone knocked at the door and opened the door, but there was still no one. After several times, finally nothing happened. The next morning, someone found a body at the foot of the mountain. After some investigation, the police took Xiaoming up the mountain. Why? It tests the potential probability of crime. The more questions you answer correctly, the more psychopathic you are, and the more likely you are to kill someone ... Six: The first question is about Xiaoming's suicide by jumping into the river. That's because when he was saving his girlfriend, he was entangled in his feet by aquatic plants. He thought it was water grass, but it was actually his girlfriend's hair. Shuang: You said he watched his girlfriend drown? Six: He didn't know before. Later, he heard the old man say that there were no aquatic plants in this river before he realized the truth and became insane. Shuang: Ah ... I see. What about the man who murdered my sister? Six: That's because her sister thinks she can meet handsome guys as long as she attends the funeral. In order to meet another handsome guy, she killed her sister when she went back to have another funeral. Shuang: Ah ... What about the one who knocked at the door in the middle of the night? Six: You are stupid. Xiaoming lives at the top of the mountain. The man who knocked at the door finally climbed to the top of the mountain. When he knocked at the door, Xiao Ming opened the door and went back to the foot of the mountain with a bang. When he climbed to the top of the mountain again, Xiaoming opened the door and fell into the foot of the mountain with a bang. After he repeated it n times, the man who knocked at the door finally couldn't hold on. He was exhausted.