大家好，小弟想请教一下关于ADV考试中63真题中的7题

a quick rule of thumb for the space required to run proc sort is:

A: two times the size of the SAS data set being sorted  
C: fourtimes the size of the SAS data set being sorted  
这个两个答案一直都拿不准。

还有第19题，
%let value=Philip;
proc print data=students;
......
run;
which where statement successfully completes the program and produces a report?

D where upcase(name)="%upcase(&Value)";
答案为D，但是我的理解，upcase的作用使字符窜大写，这里为什么没有起作用？

还有45题
to creat a list of unique customer_id values from the customer data set, which of the following techniques can be used?
1: proc sort with nodupkey and out=
2. data step with if first.customer_id=1
3. proc sql with the selcet distince statement
关于2， 需要对first变量sort 那么答案到底是 C 1 and 3 还是D  1 ,2 and 3 呢？

请问关于61题， in a data step merge, the by variable in all data set must have the same:

B  name and type   D  name type and length
关键在于这个length,如果不一样长，可以运行，但是答案中对这个表示顾虑，很多人都选了B。

不懂，帮顶！预祝考试顺利，记得回来分享啊！