The question is tough. However, it is an official question soI do not dare it is bad formulated.

Moreover, I do think your assumption is a bit off. here we are not talking about cost BUT rather loyalty of the employees recruited by the haeadhuntars.

The only way to have a workable strategy is to pinpoint those headhunters which will go out there to find those SPECIFIC worked we are looking foot. As such, the problem that those workers will leave our company is minimized due to the fact we are sure those workers have specific skills which are difficult to employed in another company. They are workers bespoke for our company. That is just A says

(B) Find out which headhunter has the highest success rate in recruiting for its clients and hire that firm.

Success rate is not what we are looking for

(C) Find out how much the company's competitors currently pay staff of the sort being sought and offer to pay prospective employees higher salaries.

Same as B for salaries

(D) Find out whether any of the company's competitors are seeking to recruit workers of the sort being sought and, if so, make sure not to hire the same headhunters that they hire.

A repeating of the stimulus, basically

(E) Find out which of the company's competitors are on the client lists of the headhunters who are being considered for the job.

We care of the workers NOT if the companies are on the list of the headhunters


Hope this helps