下面哪些定义是类型正确的？ A: f :: (Integer, Integer) - Floatf (x,y) =x / y B: f :: (Integer, Integer) - Floatf (x,y) = (fromInteger x) / (fromInteger y) C: f :: (Integer, Integer) - Floatf (x,y) = 3*x + y D: f :: (Integer, Integer) - Integerf (x, y) = 3*x + y