Which one of the following words is most similar in meaning to the word 'chasing' as used in the passage?

In the passage, 'chasing new clients' means actively seeking or pursuing new clients for business. 'Pursuing' is the closest synonym in this business context—it conveys the deliberate effort to acquire new clients. 'Running' is too literal, while 'harassing' and 'pestering' carry negative connotations not intended in the original phrase. Hence (4) Pursuing is correct.