PROC IMPORT OUT= DST.PROBLEM2
            DATAFILE= "C:\Users\xiaolin\Desktop\book.xls"
            DBMS=EXCEL REPLACE;
     SHEET="Sheet1$";
     GETNAMES=YES;
     MIXED=NO;
     SCANTEXT=YES;
     USEDATE=YES;
     SCANTIME=YES;
RUN;
data a;
set DST.PROBLEM2;
run;
proc autoreg data=a;
model vwd1=/nlag=3;/*、我想要yt=x+y(t-3),而不是yt=x+y(t-2)+y(t-2)+y(t-3),怎么改呢*/
title "The AUTOREG Procedure for VWD1";
run;
大家帮忙看看，怎么改动呢？？