做sas base题目时遇到这样一个问题，实在搞不清楚，请各位指点迷经。41.A raw data file is listed below.
1---+----10---+----20---+---
01/05/1989 Frank 11
12/25/1987 June 13
01/05/1991 Sally 9
The following SAS program is submitted using the raw data file as input:
data work.family;
infile 'file-specification';
input @1 date_of_birth mmddyy10.
@15 first_name $5.
@25 age 3;
run;
proc print data=work.family noobs;
run;
Which one of the following is the result?

Correct answer:
Values for the variable age are missing in the output because the informat for age is
coded incorrectly. Since age is standard numeric input, it should use the w.d informat to
specify a field width of 3 in the INPUT statement.

没搞明白什么意思，哪位高手给指点一下