One day Daddy and I went out    1    a walk. On the way we   2   a lot of people. We went up and   3  a look. Oh, dear!   4  did we see? There   5  a donkey(驴) in the middle of the road. It would not move. The cars and buses could not get 6  .
Then a policeman came. " 7  donkey is this?" he asked. "It' s   8   ," said a farmer, "but I   9  move it. " The policeman and the farmer did 10 best to move the donkey, but it would not move. We laughed, but the  11   of the cars and the buses were   12   . "We can't move the donkey," the farmer and the policeman said. "What shall we do?"
"Give him a carrot," my father said.
"   13 a good idea!" said the farmer.
Soon he found a   14 and showed it to the donkey. When the donkey saw a carrot, it jumped up and walked after the farmer.  15   the cars and buses could get past at last.

匀速圆周运动属于（   ）

识图析图是历史学习和历史研究的一种重要方法。右图《清时期全图》中字母④所示区域是（   ）

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已知向量$\overrightarrow{a}$=(2,1)$\overrightarrow{b}$=(-1,3)，若存在向量$\overrightarrow{c}$，使得$\overrightarrow{a}$$·$$\overrightarrow{c}$=4,$\overrightarrow{b}$$·$$\overrightarrow{c}$=-9，则向量$\overrightarrow{c}$为（　　）

He said that only after he went abroad _______ what his motherland meant to him.