几题sas base 123题疑问

几题sas base 123题疑问
我没有答案解析,很纠结.先谢谢大神.
1. The contents of the raw data file FURNITURE are listed below:
----|----10---|----20---|----30
chair,table
chair,couch,table
The following SAS program is submitted:
data stock;
infile 'furniture' dsd;
input item1 $ item2 $ item3 $;
run;
Which one of the following is the value of the variable named ITEM2 in the first observation of the output data set?
A. table
B. ,table
C. . (missing numeric value)
D. ' ' (missing character value)
Answer: D
为什么是D不是dsd就应该skip那个missing value 么
2.The following SAS program is submitted:
data allobs;
set sasdata.origin (firstobs = 75 obs = 499);
run;
The SAS data set SASDATA.ORIGIN contains 1000 observations.
How many observations does the ALLOBS data set contain?
A. 424
B. 425
C. 499
D. 1000
Answer: B
为什么是B不是C呢
3.The SASDATA.BANKS data set has five observations when the following SAS program is submitted:
libnamesasdata 'SAS-date-library';
data allobs;
set sasdata.banks;
capital=0;
do year = 2000 to 2020 by 5;
capital + ((capital+2000) * rate);
output;
end;
How many observations will the ALLOBS data set contain?
A. 5
B. 15
C. 20
D. 25
Answer: D （为什么为什么?!）
4.The following SAS program is submitted:
data work.test;
First = 'Ipswich, England';
City_Country= substr(First,1,7)!', '!'England';
run;
Which one of the following is the length of the variable CITY_COUNTRY in the
output data set?
A. 6
B. 7
C. 17
D. 25
Answer: D 不懂呀!
另外大家知道哪里看解析?谢谢网友先! =)
2,3,4都明白了.只回答1就好啦!还有哪里可以看explanation啊.

因为DSD默认分隔符为逗号, 而读取的时候如果是连续两个分隔符则显示为缺失!
想学好SAS可以来贴吧坐坐!http://tieba.baidu.com/f?kw=sas%B1%E0%B3%CC&fr=index