Write a question about the following article.

I then went in to a computer and they had me put in my personal info . ( Name , address , past jobs , etc . ) After I finished that , I went to another section where I had to answer questions . They said something like , " My crack use affects my job " or " My meth use affects my job " , and you had to pick one answer , such as " Yes , it affects my job " to " I ' ve never used this illegal drug . "

Question:
What may be the reason for them participating in the study ?
OPT:
[a]. They had been offered pay to do it .;
[b]. None of the above choices .;
[c]. They enjoy doing research studies .;
[d]. They wanted to help out the company .;