67.Consider the following data step:

  data WORK.NEW;
     set WORK.OLD(keep=X);
     if X < 10 then X=1;
     else if X >= 10 AND X LT 20 then X=2;
     else X=3;
  run;

In filtering the values of the variable X in data set WORK.OLD, what value new value would be assigned to X if its original value was a missing value?

     A. X would get a value of 1.
     B. X would get a value of 3.
     C. X would retain its original value of missing.
     D. This step does not run because of syntax errors.

Answer: A

如果是缺失值，那么在排序过程中是默认为最小。
大家可以用proc sort 过程来测试一组有缺失值的数据，就知道排在最小的观测的是缺失值。

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