During the compilation phase of a DATA step, which of the following is true?

During the compilation phase of a DATA step, it is necessary to define and assign variables in order for the program to run correctly. This phase involves preparing the code for execution, where the SAS system verifies the existence of variables and allocates memory for them. When you define a variable, you essentially convey to SAS what data it should expect and how much space it will need to store that data.

The compilation phase does not maintain variable values from previous steps, as it works with the current DATA step rather than any prior state. Temporary variable assignments are made during the execution phase rather than finalized in the compilation phase. While output is indeed conditional upon the presence of errors during execution, this concern is more relevant to the execution phase rather than the compilation phase itself.

Thus, the correct understanding of the compilation phase is focused on the necessity to define and assign variables, making option B the appropriate choice.