In a large mixing bowl, stir together the sugar and flour. Stir in rhubarb, raspberries and apple. Transfer to a pastry-lined 9-inch pie plate. Trim pastry even with the rim of the plate. Cut slits in the top crust and place top crust over fruit filling in plate. Seal and flute the edge.
     Cover edges with foil and bake at 375 degrees for 25 minutes. Remove the foil and bake another 20 to 25 minutes until top is golden and fruit is tender. Cool on wire rack.