如图，△ABC中，点D、E分别为AB、AC上的点，且满足DE∥BC，若AD=3，BD=2，AE=2，则EC的长为（　　）

    The giraffe is the tallest modern land animal. It can be over 5. 5 meters tall. Its neck alone may be 1. 9 meters long. Yet the giraffe has only seven bones in its neck, the same number as in the humans'. Even a small bird has many more bones in its neck than a tall giraffe. Each bone in a giraffe's neck is very long, while the bones in a human's neck are short. That makes the difference. A female giraffe gives birth to one baby at a time. The baby, called a calf, is about 1. 9 meters tall at birth. By the age of eight it is full-grown. The giraffe eats mostly leaves. Because it has a long neck, it can reach the high leaves on the trees.

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已知坐标平面内的三个点A（1，3），B（3，1），O（0，0），求△ABO的面积．