data benny10 ;
input group  return@@;
cards;
1 12
1 15
1 10
1 22
1 21
2 30
2 22
2 15
2 23
2 15
3 10
3 9
3 13
3 15
4 20
4 22
4 23
4 25
4 20
4 26
;
proc glm;
class group;
model return=group;
means group/snk;
run;

You may either estimate or lsmean statement.
data return;
input group return;
cards;
1 12
1 15
1 10
1 22
1 21
2 30
2 22
2 15
2 23
2 15
3 10
3 9
3 13
3 15
4 20
4 22
4 23
4 25
4 20
4 26
;
proc glm data=return;
class group;
model return=group/solution noint;
lsmeans group / pdiff tdiff;
estimate 'G1 VS G2' Group 1 -1 0 0;
estimate 'G3 VS G4' Group 0 0 1 -1;
run;
quit;

谢谢各位前辈的指教，我会试试的，但也希望有更多的方法可以让我试试!