Good habits are important to us. We should build good living habits. Now let's have a look at the two brothers. Li Qiang and Li Gang are brothers. But their living habits are different. Now let's go to Li Qiang's room. Li Qiang cleans his bedroom every day and puts his things away. Look! There is a computer on the desk. There are two balls under the bed. A guitar and a kite are on the wall. Some books are on the shelf. So he must be a careful boy. Now let's go to Li Gang's room. The room is not clean. Can we see his clothes on the desk? Oh, yes. We can see a football and a knife on the desk, too. Li Gang never does any cleaning on weekends. So his room is in a mess.

    What do you think of Li Qiang and Li Gang? Li Qiang is a good boy. Li Gang must learn from his brother

在数学课上，老师提出如下问题：

已知：如图， $△ABC$ 及 $AC$ 边的中点 $O$ ．

求作：平行四边形 $ABCD$ ．

①连接 $BO$ 并延长，在延长线上截取 $OD=BO$ ；

②连接 $DA$ 、 $DC$ ．

所以四边形 $ABCD$ 就是所求作的平行四边形．

老师说：“小敏的作法正确．

请回答：小敏的作法正确的理由是____．

——          ? 

——He is tall and of medium build.

东南亚主要由（　　）