答案是D。

data test;
    set sashelp.class;
    *** It can be used in an if/thencondition;
    if _error_=0 then put "Observation" _n_;

    *** It can be used in an assignmentstatement. ;
    var=_error_;

     *** It cannot be put into a keep statementor keep= option. ;
          keep name age height _error_; /*This will cause an WARNING message in the log.*/

    *** It is automatically dropped;
        * The dataset TEST doesn't have the variable _error_;
run;

多谢啦！！！！！！！！！！！！！！！！！！！！！！！1

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