52.Given the SAS dataset WORK.EMP_NAME:

  Name EmpID

  ---- -----

  Jill  1864

  Jack  2121

  Joan  4698

  John  5463

Given the SAS data setWORK.EMP_DEPT:

  EmpID Department

  ----- ----------

   2121 Accounting

   3567 Finance

   4698 Marketing

   5463 Accounting

The following programis submitted:

  data WORK.ALL;

     merge WORK.EMP_NAME(in=Emp_N)

           WORK.EMP_DEPT(in=Emp_D);

     by Empid;

     if (Emp_N and not Emp_D) or (Emp_D and notEmp_N);

  run;

How many observationsare in data set WORK.ALL after submitting the program?

     A. 1

     B. 2

     C. 3

     D. 5

为什么选B，merge语句如何得到两个观测的？