What Is the Key Difference Between Professional Search Firms and Placement

What is the key difference between professional search firms and placement agencies?

A) placement agencies can be more objective than search firms
B) the cost per recruit when using placement agencies is lower than it is when using search firms
C) the overall success rate in recruiting the right person is higher when using placement agencies as opposed to search firms
D) agencies use advertising to attract applicants whereas search firms seek out recruits from among other organizations' employees
E) agencies have a greater understanding of niche requirements in specific industries than search firms