Test your love fate and test your stubbornness index in love

This is a psychological test with a story, testing your stubbornness index in love~ Let's calm down and start~~

Test Start

Imagine that you are a famous detective. One day you receive a phone call reporting that a murder has occurred on the 5th floor of a commercial building, and you are asked to go over and investigate and sort out the case.
When you arrive at the 5th floor of the building, you find a man named A standing at the door in a daze, aimlessly. His eyes were dull, and he kept pacing back and forth at the door, muttering something to himself. He seemed very nervous, as if he had done something wrong and was afraid of being discovered.
At this time, the company's manager, Mr. B, comes towards you and, seeing that you are a famous detective, begins to explain to you in detail what has just happened. The manager spoke in a very clear and logical manner, even explaining the details of the murder case, but there was no trace of nervousness in his eyes, as if no murder had ever happened here. Such actions make you increasingly suspicious, wondering if he planned all this.
When we arrived at the crime scene, we found it in a mess. One of the people was the company secretary Ms. C. Her hands were covered in blood and she was sitting on the ground with a knife in her hand. When she saw you come in, her eyes flashed with murderous intent and she stared at you viciously, never taking her eyes off you.
There were two people lying on the floor, both of them were disheveled and covered with wounds. The difference is that one of them is the company's client and the protagonist of the murder case, Yamamoto Taro, who is already dead. The other is Mr. D, an employee of the company. Although he also fainted due to injuries, his life is not in danger.
According to the surveillance video reviewed by the police, there were only these four people in the company when the murder occurred, and no one else entered or left. So, even though there is still a lot of missing evidence, who would you identify as the most likely murderer based on your first impression?

A: People who kill someone for the first time must be at a loss.
Mr. B: He was so calm even after a murder. There must be a ghost.
Mr. C: The evidence is all in our hands, how can we be wrong?
Mr. D: The reason is very clear. The two of them had an argument and fought each other, and Taro Yamamoto was killed by mistake. Now, answer my question: Who is most likely the murderer? Find the answer that corresponds to your option.