When the president was Yoweri Museveni, and the year was 1993, with rank of 6 under political rights, what was the total of civil liberties?
CREATE TABLE "historical_rankings" (
  "year" real,
  "political_rights" real,
  "civil_liberties" real,
  "status" text,
  "president" text
);
SELECT SUM("civil_liberties") FROM "historical_rankings" WHERE "political_rights"=6 AND "president"='yoweri museveni' AND "year"=1993;