Why do market research companies temporarily recruit a large number of investigators?

Make up for one's own shortage of personnel. "Why do market research companies temporarily recruit a large number of investigators" is a multiple-choice question in the autumn 2020 market research and analysis paper of Yunnan Open University. The options of this question are: improving the quality of personnel, making up for the shortage of their own personnel, introducing talents and enriching human resources. According to the professional knowledge of market research and analysis, the answer to this question is to make up for the shortage of personnel.