Name the average Against that has a Venue of twickenham , london on 25 november 1978?
CREATE TABLE "matches" (
  "opposing_team" text,
  "against" real,
  "date" text,
  "venue" text,
  "status" text
);
SELECT AVG("against") FROM "matches" WHERE "venue"='twickenham , london' AND "date"='25 november 1978';