单项选择题

下列程序段的输出结果是 CLEAR STORE 10 TO A STORE 20 TO B SET UDFPARMS TO REFERENCE DO SWAP WITH A,(B) A,B PROCEDURE SWAP PARAMETERS Xl,X2 TEMP=X1 Xl=X2 X2=TEMP ENDPROC

A.10 20
B.20 20
C.20 10
D.10 10