My Favourite Apple Crisp Topping

1 cup uncooked rolled oats
1/2 cup sifted enriched flour
1 cup firmly packed brown sugar
1/2 cup butter or margarine

Mix oats, flour and brown sugar.  Cut in butter until crumbly.  Top sliced apples with this mixture.  Bake in a moderate oven (350 F) until apples are tender.