一道sas base programming 的题

一道sas base programming 的题
The following SAS program is submitted:
data_null_;
set old;
put sales1 sales2;
run;
Where is the output written?
A. the SAS log
B. the raw data file that was opened last
C. the SAS output window or an output file
D. the data set mentioned in the DATA statement
Answer: A
为什麽答案是A?
谢谢!