设；则和的夹角θ为（）．
参考答案：135°
He accidentally________he had quarreled with his wife and then he hadn't been home for a long time.[ ]
A. let down
B. let in
C. let off
D. let out
此时最紧迫的抢救措施是
A．请胸外科医师会诊处理B．清除上呼吸道异物，保持呼吸道通畅C．输血D．吸氧E．左下肢夹板固定
；则
和
的夹角θ为（）．
；则和的夹角θ为（）．