留些欢乐在心中，会让人生更乐观;留些梦想在心中，会让生活更有追求;留些勇气在心中，会在遇到困难时更坚强。

请以“留些______在心中”为题，写一篇文章。

要求：①篇幅600字以上，除诗歌外，文体不限。②思想内容健康向上。③文中不得出现真实的地名、校名、人名。

牛的细胞生命活动的控制中心是

阅读理解

      Mr. Smith made many tests with different animals and the monkey was the cleverest of all the animals.

      One day Mr. Smith put a monkey in a room. He also put some small boxes in it. In one of the boxes there was some food. "How long will it take the monkey to find the food?" Mr. Smith said to himself. "Let me wait and see." He left the room and waited outside. Three minutes later, he put his eye to the keyhole. What did he see? He saw the eye of the monkey. The monkey was on the other side of the door and looked at Mr. Smith through the keyhole.

①私营经济

②集体经济

③国有经济

④个体经济