单项选择题 设有一个关系Student(学号，姓名，系名，课程号，成绩)，查询至少选修了四门课程的学生学号、姓名及平时成绩的SELECT语句应该是： SELECT学号，姓名，AVG(成绩) AS平均成绩 FROM Student GROUP BY (1) HAVING (2)(15)

未知题型 听力原文：Police Officer: Hello. 24th Precinct. Officer Jones speaking.Man: Help. Yeah，uh，it was wild，I mean really bizarre.Police Officer: Calm down sir!Now，what do you want to report?Man: Well，I'd like to report a UFO sighting.Police Officer: A what?Man；What do you mean“what”?An unidentified flying object!Police Officer: Wait，tell me exactly what you saw.Man: Well，I was driving home from a party about three hours ago，so it was about 2:00 AM，when I saw this bright light overhead.Police Officer: Okay. And then what happened?Man: Oh，man. Well，it was out of this world. I stopped to watch the light when it disappeared behind a hill about a kilometer ahead of me.Police Officer: Alright. Then what?Man: Well，I got back in my car and I started driving toward where the UFO landed.Police Officer: Now，how do you know it was a UFO?Perhaps you only saw the lights of an airplane，or the headlights of an approaching car. Things like that happen. you know.Man: Well if it was that，how do you explain“the BEAST”?Police Officer: What do you mean，“the BEAST”?Man: Okay. I kept driving for about five minutes when all of a sudden，this giant，hairy creature jumped out in front of my car.Police Officer: Oh，yeah. Then what?Man: Well，then，the beast picked up the front of my car and said，“Get out of the car. I'm taking you to my master!”Something like that.Police Officer: Wow?A hairy alien who can speak English!Come on!Man: I'm not making this up，if that's what you're suggesting. Then，when I didn't get out of the car，the beast opened the car door,carried me on his shoulders to this round-shaped flying saucer，and well，that's when I woke up along side the road. The beast must have knocked me out and left me there.Police Officer: Well，that's the best story I've heard all night，sir. Now，have you been taking any medication，drugs，or alcohol in the last 24 hours?You mentioned you went to a party.Man: What?Well，I did have a few beers，but I'm telling the truth.Police Officer: Okay，okay. We have a great therapist that deals with THESE kinds of cases.Man: I'm not crazy.Police Officer: Well，we'll look into your story. Thank you.(23)A．about 12:00 AMB．about 3:00 AMC．about 5:00 AMD．about 24:00

未知题型 下列平衡梁的形式中，（ ）是用无缝钢管、吊耳、加强板等焊接而成，可用于吊装排管、钢结构件及中、小型设备。