data pro;
input year 1-2 prod 3-7 @;
title '某厂1984-1990年度产值的曲线图'；
cards;
84 24334 85 32424 86 34234 87 24345 88 24343 89 34353 90 23123;
proc sort; by year;
run;

显示：
ERROR: No CARDS or INFILE statement.
NOTE: The SAS System stopped processing this step because of errors.
WARNING: The data set WORK.PRO may be incomplete.  When this step was stopped there were 0
         observations and 2 variables.
WARNING: Data set WORK.PRO was not replaced because this step was stopped.
NOTE: DATA statement used:
      real time           0.01 seconds
      cpu time            0.01 seconds

422  proc sort; by year;
ERROR: Variable YEAR not found.
423  run;

我是sas的初学者，不知道问题出在哪，劳烦各位帮忙解答，谢谢