分层抽样 （stratified sampling)

B．They both need a sampling frame of each of the subgroups of the target population.

C．In both of them,researchers want to ensure that all strata are included in the sample in order to enhance the representativeness of the sample and/or to enable comparisons between strA

D．Stratified sampling does not need a sampling frame to generate a stratified sampl

E．

E．In both of them,once the sample number of each subgroup is defined,samples are drawn in simple random sampling or systematic sampling metho

D．

A. Tom and Sam

B. Tom’s and Sam

C. Tom and Sam’s

D. Tom’s and Sam’s

SAM现象(名词解释)

A.SIP

B.SEP

C.PES

D.PIS

E.PAS

A.HCU\SAM\SAM\Domains\Account\Users\Names

B.HCR\SAM\SAM\Domains\Account\Users\Names

C.HLM\SAM\SAM\Domains\Account\Users\Names

D.HCR\SAM\Domains\Account\Users\Names

以下哪条命令可以改变文件file的所有者为Sam()？

A.chmod Sam file

B.chown Sam file

C.chgrp Sam file

D.umask Sam file