写一个程序，定义抽象基类Shape，由它派生出3个派生类: Circle(圆形)、Rectangle(矩形)、Triangle(三角形)，用一个函数printArea分别输出以上三者的面积，3个图形的数据在定义对象时给定。

下面是一个Python的实现示例：

from abc import ABC, abstractmethod
import math

class Shape(ABC):
    @abstractmethod
    def area(self):
        pass

class Circle(Shape):
    def __init__(self, radius):
        self.radius = radius
    
    def area(self):
        return math.pi * self.radius ** 2

class Rectangle(Shape):
    def __init__(self, length, width):
        self.length = length
        self.width = width
    
    def area(self):
        return self.length * self.width

class Triangle(Shape):
    def __init__(self, base, height):
        self.base = base
        self.height = height
    
    def area(self):
        return 0.5 * self.base * self.height

def printArea(shape):
    print("The area of the shape is:", shape.area())

# Example usage
circle = Circle(5)
rectangle = Rectangle(3, 4)
triangle = Triangle(2, 6)

printArea(circle)     # Output: The area of the shape is: 78.53981633974483
printArea(rectangle)  # Output: The area of the shape is: 12
printArea(triangle)   # Output: The area of the shape is: 6.0

这个程序实现了一个抽象基类`Shape`，其中定义了一个抽象方法`area()`。`Circle`、`Rectangle`和`Triangle`分别继承了`Shape`，并实现了自己的`area()`方法。在`printArea()`函数中，我们可以传入任何一个继承自`Shape`的对象，然后输出它的面积。