Given $\overline{a}$ = $p_{r}\overline{a}_{r}$ = $p_{nr}\overline{a}_{nr}$ , Where a Is the Overall Mean and "R" Refers

Given $\overline{a}$ = $p_{r}\overline{a}_{r}$ = $p_{nr}\overline{a}_{nr}$ , where a is the overall mean and "r" refers to those responding and "nr" to those not responding, which of the following statements is most correct?

A) Both $\overline{a}_{r}$ and $\overline{a}_{nr}$ can be calculated by splitting up a (which is known or can be estimated) into its component parts.
B) The nonresponse component can be ignored as it is reasonable that $\overline{a}_{r}$ equals $\overline{a}_{nr}$ .
C) $\overline{a}$ cannot be calculated because of the difficulty in estimating $\overline{a}_{r}$ and $\overline{a}_{nr}$ .
D) A rough estimate of $\overline{a}$ can be made by adjusting the initial results after $\overline{a}$ is estimated by follow-up.
E) A rough estimate of $\overline{a}$ can be made by adjusting the initial results after $\overline{a}_{nr}$ is estimated by follow-up.