Which of the following holds a line of raw data across multiple iterations of the DATA step?

The choice that holds a line of raw data across multiple iterations of the DATA step is indeed represented by the double at sign (@@). This operator allows the SAS DATA step to read data records that span multiple lines in a single iteration. When using @@, SAS continues to read data until all the variables specified in the INPUT statement have been filled or until it encounters an END statement in the DATA step.

For example, if your raw data has been structured in such a way that multiple data values are presented after line breaks, SAS uses this operator to ensure that it considers the subsequent lines as part of the same input record until it completes reading the specified variables.

In contrast, the single at sign (@) is intended for use with temporary line holds but doesn't allow for holding data across multiple iterations; it is primarily used to hold the line for further processing within the same iteration. The option representing a forward slash (/) is typically used to signal a new line of data in the input, essentially breaking the current line and starting fresh for the next. Finally, the MISSOVER option is utilized to handle situations where an input line might contain fewer values than expected, assigning missing values instead of moving to a new line.

Thus, @@ is the appropriate choice