某人从A点出发向西走了10m，到达B点，然后改变方向按西偏北60°走了15m到达C点，最后又向东走了10米到达D点．

（1）作出向量$\overrightarrow{AB}$，$\overrightarrow{BC}$，$\overrightarrow{CD}$（用1cm长的线段代表10m长）

（2）求|$\overrightarrow{DA}$|．

    This story is about a young man. He worked very hard at his lessons, so he was too busy to have a rest. At last, he couldn't go to sleep every night. When he went to bed, he closed his eyes and tried to sleep.But the more he tried, the more he stayed awake.

    After a while, he decided to visit the doctor."I just can't go to sleep at night. What should I do?" "I have a suggestion,"said the doctor, "try counting numbers. By the time you reach one thousand, you'll be asleep. I'm sure of it. The next day the man returned to the doctor's office."well," said the doctor, "How are you today? Did you try my suggestion?"

    The man still looked tired, "Yes,"he said, " I tried counting one, two, three…up to one thousand. But when I reached five thousand and sixty-nine, I began to feel sleepy. I had to get up and drink some tea so that I could go on counting up to one thousand, but then I still couldn't fall asleep.