CREATE TABLE table_31553 ("Date" TEXT, "Venue" TEXT, "Score" TEXT, "Result" TEXT, "Competition" TEXT)

What score did vasil levski national stadium, sofia, which was friendly during competition, earn?
SELECT "Score" FROM table_31553 WHERE "Competition" = 'friendly' AND "Venue" = 'vasil levski national stadium, sofia'
SELECT "Score" FROM "table_31553" WHERE "Competition" = 'friendly' AND "Venue" = 'vasil levski national stadium, sofia'