Question: In which city is the main management office of the company that owns J. Walter Thompson located?
Sentence (from "WPP plc"): It owns a number of advertising, public relations and market research networks, including IMRB, Millward Brown, Grey, Burson-Marsteller, Hill & Knowlton, JWT, Ogilvy & Mather, TNS, Young & Rubicam and Cohn & Wolfe.
Relevant evidence: No