大家好，我有以下程序。已知sample.xls里确实有mir-1246和sheet2这两个sheet，r1和r2能够正确生成，但是r3不能。请问这是怎么回事，如果想按生成r3的代码风格来写，应该怎样做？
libname d excel 'E:\Sample.xls';

%let sheets = mir-1246 sheet2;

data r1;
set d.'mir-1246$'n;
run;

%let sheet = d.'mir-1246$'n;
data r2;
set &sheet;
run;

%let sheetname = d.%quote(%'%scan(&sheets,1,%str( ))$%'n);
data r3;
set &sheetname;
run;