exmaple 1:

%let Mv=shoes;
%macro Product(Mv=bike);
   %let Mv=clothes;
%mend;

%Product(Mv=tents)
%put Mv is &Mv;


Example 2:
%let a=cat;
%macro animal;
   %let a =dog;
%mend;
%animal
%put a is &a

第一题应该是输出 Mv is shoes.
第二题输出         a is dog.
我想知道为什么第二题的答案不是 a is cat.

thx a lot.