CREATE TABLE table_49573 ("Date" TEXT, "Place" TEXT, "Race winners" TEXT, "GP winner" TEXT, "Source" TEXT)

What source has a race winner of ben adriaenssen / ben van den bogaart, and the gp winner of ben adriaenssen / ben van den bogaart, for the date of 1 april?
SELECT "Source" FROM table_49573 WHERE "Race winners" = 'ben adriaenssen / ben van den bogaart' AND "GP winner" = 'ben adriaenssen / ben van den bogaart' AND "Date" = '1 april'
SELECT "Source" FROM "table_49573" WHERE "Date" = '1 april' AND "GP winner" = 'ben adriaenssen / ben van den bogaart' AND "Race winners" = 'ben adriaenssen / ben van den bogaart'