CREATE TABLE table_55559 ("Date" TEXT, "Opponent" TEXT, "Venue" TEXT, "Result" TEXT, "Attendance" FLOAT)

Which Date has an Opponent of manchester united, and a Venue A?
SELECT "Date" FROM table_55559 WHERE "Opponent" = 'manchester united' AND "Venue" = 'a'
SELECT "Date" FROM "table_55559" WHERE "Opponent" = 'manchester united' AND "Venue" = 'a'