SAS新手求助

The following SAS program is submitted:
data numrecords;
infile 'file-specification';
input @1 patient $15.
relative $ 16-26 @;
if relative = 'children' then
input @54 diagnosis $15. @;
else if relative = 'parents' then
input @28 doctor $15.
clinic $ 44-53
@54 diagnosis $15. @;
input age;
run;
How many raw data records are read during each iteration of the DATA step during execution?
A. 1
B. 2
C. 3
D. 4

怎么看iteration啊 跟@有什么关系

它是什么意思呢 跪求指导

自己顶