The following SAS program is submitted:

  data WORK.TWO;

     set WORK.ONE;

     Total=mean(of Rev:);

  run;

What value will SAS assign to Total?

     A. 3

     B. 1.6

     C. 4.8

     D. The program fails to execute due to errors.

我知道of后面可以跟一个向量，可是Rev:是怎样一个用法？