The following SAS program is submitted:

data WORK.LOOP;  X = 0;  do Index = 1 to 5  by  2;    X = Index;  end;run;

Upon completion of execution, what are the values of the variables X and Index in the SAS data set named WORK.LOOP?

• X = 3, Index = 5
• X = 5, Index = 5
• X = 5, Index = 6
• X = 5, Index = 7
  

答案是4，可为什么Index在这里是7呢？百思不得其解，跪求大神解惑！谢谢~