Who are all hosts when men's singles is Ma Wenge?
CREATE TABLE "senior_events" (
  "season" text,
  "host" text,
  "mens_singles" text,
  "womens_singles" text,
  "mens_doubles" text,
  "womens_doubles" text
);
SELECT "host" FROM "senior_events" WHERE "mens_singles"='Ma Wenge';