这是第32题的问题和答案选项：
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.

Answer: C

我觉得32题的答案应该是b吧，而不是c.在compilation阶段不论是automatic variable还是普通的variable在pdv里应该都是显示为空的吧，然后当execution阶段开始时automatic variable的_N_为1,_ERROR_为0,普通variable为missing, sum语句或retain语句的variable在第一次iteration时的初始值也是missing吧,除非有特别的赋值，然后之后的iteration里才会保留数值。
准备下周就考试了，希望各位前辈能够解答下我的疑惑。