各种抽样方法的抽样误差一般是( )。

A．单纯随机抽样≥整群抽样≥系统抽样≥分层抽样

B．整群抽样≥系统抽样≥单纯随机抽样≥分层抽样

C．整群抽样≥单纯随机抽样≥系统抽样≥分层抽样

D．分层抽样≥单纯随机抽样≥系统抽样≥整群抽样

The manager urged older staff ____early retirement and new staff _______ more time for work.

A. take up; to set aside              B. took up; set aside   

C. would take up; to lay aside        C. must take up; lay aside