大家好 ，我有些疑惑究竟什么时候infile后应该加''（单引号）, 什么时候不需要加呢？可以结合下面这道题去分析吗？谢谢

The following SAS program is submitted:

libname  rawdata1  'location of SAS data library';filename  rawdata2  'location of raw data file';data work.testdata;    infile <insert item here>    input sales1 salse2;run;

Which one of the following is needed to complete the program correctly?

A. rawdata1
B. rawdata2
C. ‘rawdata1′
D. ‘rawdata2′