What statement is used to sort the variable Salary in ascending order in the highlighted SAS program?

The statement used to sort the variable Salary in ascending order is "BY Salary." This is part of the DATA step and PROC SORT in SAS, which is specifically designed to manage the sorting of data sets.

When you use the "BY" statement in conjunction with PROC SORT, SAS recognizes that you want to sort the dataset according to the specified variable(s). By default, this sorting is done in ascending order unless otherwise specified. Thus, utilizing "BY Salary" efficiently instructs SAS to organize the dataset based on the values in the Salary variable from the lowest to the highest.

Other choices suggest different syntax or commands that are not recognized in SAS for sorting datasets, which is why they do not serve the intended purpose in this context. The inherent structure of SAS commands necessitates using the syntax associated with its respective functionalities for proper execution.