Which of the Following Is TRUE

Which of the following is TRUE?

A) When sampling from a population that is highly skewed, a cluster sample generally provides the most representative sample.
B) Stratified sampling is a very useful sampling technique. It allows closer examination of the characteristics of particular subgroups. It also lowers the chance of error by ensuring that subgroups are adequately represented in the sample. However, this method generally produces less precise estimates of population values than simple random samples.
C) In calculating the standard error of the mean when using a stratified sample, one finds that differences among strata means do not enter the estimate.
D) When using proportional allocation in stratified random sampling, one samples from each of the strata in proportion to their respective variabilities.
E) The sampling distribution of means for stratified sampling is generally less concentrated than that obtained from simple random sampling.