"Look at the eighteenth question: the end point of a vector is B(2,-1,7), and its projection on the X, Y, and Z axes is 4, -4, and 7 in turn, and find the coordinates of the starting point A of this vector." After reading the question, Professor Kishi began to explain the solution: "It's very simple, as long as we set the coordinates of point A as (X, Y, Z), then what is the vector AB?" Yes, it is the coordinates of point B minus the coordinates of point A, which is equal to (4,-4,7), and the result is equal to what is the value? ”

"(-2,3,0)" I replied first, and strangely enough, none of the other students spoke again, except for the other three people in our dormitory, who said yes one after another. In the past, students were very active in expressing their answers.

Professor Kishi listened to my answer, neither right nor wrong, she propped her hands on the desk, leaning her upper body unresponsive. After a moment, she said: "The end point of a vector is B(2,-1,7), and its projection on the X, Y, and Z axes is 4, -4, and 7 in turn, and the coordinates of the starting point A of this vector are found." Let's just set the coordinates of point A to ······"

"Did the teacher just talk about this question?" Xiao Zhao touched me with his elbow.

"Yes." An ominous premonition came over me, and my heart beat heavier and heavier.

"The teacher and classmates are weird." Xiao Yi put down the textbook and looked around.

Yes, it's all weird - Professor Kishi held the podium, neither changed his movements nor changed his tone, and persistently talked about her AB points, and the students did not use their pens or turn the books, but only looked at the textbooks with their eyes. I don't know if it's my delusion, but I feel that the light in the whole classroom seems to be weaker than just now, and it's dark, and it's a sunny summer noon. What's even more bizarre is that those black fogs seem to have life, crawling towards people in wisps.

"Stand on the table!" I saw the black fog spreading on the ground, and my body reacted first, jumping onto the table. He was followed by Xiao Yi, "Bang! With a sound, Xiao Zhao climbed up with his legs and arms, and he looked very panicked. Only Xiaobai didn't know why, "Huh? He was still standing there, looking up at us, his eyes full of confusion and surprise. I was closest to him, reached out and pulled him to the table, and said, "What are you doing, you guys?" ”

"It's weird." Xiao Zhao muttered.

Yes, how strange it is, even if we made such a big noise, none of the teachers and classmates cared, one tirelessly repeated the AB point, and the group tirelessly listened to it. Xiaobai also noticed that something was wrong, but he was still at a loss.

"Run!" Xiao Yi said suddenly.

"How do you run?" Xiao Zhao asked.

"Go from above!" I said. It's a bit of a crazy move — four college students suddenly run out of the classroom with their desks in the middle of class, and if it's on the news, it's a discussion about college students' stress tolerance and psychological vulnerability.

The black fog has risen to the table and is trying to drill into our noses. By this time we had run to the first row of tables, the last table we could use, and I jumped off the table after a short pause, ran past the classroom door, and when I got to them, I backed out of the door and rushed out.

What's going on outside? I don't know, I can only follow the only command of my brain: rush out! Get out of this classroom! What if the situation outside the classroom was the same as inside the classroom? As soon as we went out, we would lose our legs in the black fog, and I was faintly afraid of this, but I really didn't want to worry about it so much at such an urgent juncture.

The door slammed open, and my assumption was true!

"Did we talk about that last time?"

"Question 18." The classmates returned in a sparse manner.

"Eighteen questions are finished, right?"

"That's it."

"Great, I don't know what's going on today, and I'm annoyed when I see eighteen questions. Let's move on to the next question. ”