正扣安全接头对扣后要加压（）kN，并缓慢向左转动，上紧安全接头。
A、1
B、10
C、30
D、40
参考答案：B
看图完成对话。
D: Hi, Tim, can you play soccer ____1____ me ____2____ Saturday?
T: I'm sorry I ____3____. I have too ____4____ homework to do this weekend.
D: That's too ____5____. Maybe ____6____time.
T: Sure, Dave. Thanks for ____7____.
21+46+89+54=（□+□）+（□+□）
