What effect do the DROP= and KEEP= data set options have?

The correct choice highlights that the DROP= and KEEP= data set options fundamentally alter which variables appear in the output data set. The DROP= option explicitly removes specified variables from the data set, meaning those variables will not be present in the resulting data set. Conversely, the KEEP= option allows only the specified variables to appear in the output, meaning all other variables are excluded from the data set.

This distinction is essential for managing and tailoring the data you work with in SAS. By using DROP=, you can streamline your data by excluding unnecessary variables while retaining those that are vital to your analysis. On the other hand, KEEP= is useful when you want to focus exclusively on a few variables while disregarding the rest.

In summary, the correct answer captures the functionality of these options accurately, while other alternatives misrepresent their behaviors, such as suggesting that KEEP= excludes specific variables or that both require variable redefinitions, which is not the case. The DROP= and KEEP= options straightforwardly dictate visibility in the dataset without needing to redefine variables.