简述加权最小二乘法的思想。
参考答案：
对于存在异方差的模型，用某一权数对样本观测值或残差加权，再使用普通最小二乘法估计模型参数
When we climbed up to the top of the mountain, we were all __________ ,but we were very happy.
A．out of sight
B．out of reach
C．out of breath
D．out of danger
肱骨中段粉碎性骨折，选用哪种手术方法较好
A．加压钢板固定
B．髓内针固定
C．手法复位，夹板固定
D．普通钢板固定
E．骨牵引治疗
