Q. It is the custom of a company to avoid to say 'No' to any person who approaches it to. Rather it gets his application and tells him that as and when company required his service will be called . In this way, company acquired a database. Its advantage is that at the time of suitable applicant out of the database can called for interview. Thus the company saved  from expenses on advertisement .

Identify the source of recruitment referred to in the above pqaragarph.