He spoke English so well _____ by us all.

A．to be praised

B．as to be praised

C．for being praised

D．that was praised

抽样时先按照某些人口学特征或某些标志将研究人群分为若干层，然后从每层抽取随机样本的抽样方法称为

A．单纯随机抽样

B．系统抽样

C．分层抽样

D．整群抽样

E．多级抽样