Base 70里的第32题! 求解答

32.Consider the following data step:

data WORK.NEW;
    set WORK.OLD;
    Count+1;
run;

The variable Count is created using a sum statement. Which statement regarding this variable is true?
     A. It is assigned a value 0 when the data step begins execution.
     B. It is assigned a value of missing when the data step begins execution.
     C. It is assigned a value 0 at compile time.
     D. It is assigned a value of missing at compile time.


为什么答案是C ？？？？？？？


据我所知，compile阶段只是检查语句是否错误而已，并没有进行赋值的。只有在execution的阶段才开始赋值的吧？？？

count在数据步的编译（compile）过程中，初始值就默认为0，且只能为0了。