The best use of the set of questionnaires completed during job analyses by human resources would be to compare the level of responsibilities required in different jobs at the same level. This can help in creating job descriptions, defining roles and responsibilities, setting standards for performance evaluation, and determining pay scales. The information obtained from the job analysis questionnaires can also be used to identify any gaps in skills or knowledge required for a job and create training and development plans to fill these gaps. Therefore, option C is the correct answer.
Using the set of questionnaires to develop a plan to sell the company (option A) or using them instead of conducting employee evaluations (Option D) are not appropriate uses for the job analysis questionnaires. Option B suggests using the questionnaires to recruit workers with additional experience, but this may not be the most effective use of the questionnaires as they are generally used to define job requirements rather than to identify candidates with specific experience.