Many years ago，there lived a rich man who wanted to help the people of his town．But first he wanted to find out whether they deserved（应得到）his help．So he placed a very large stone in th
In ancient times, dogs were mainly ______helping people hunt( 打猎) .Now they are more useful-they can help the blinds, search for the bad eggs.A．bad forB．used toC．used forD．good at
Look at this photo of my family. There are six people in my family. This woman is my mother. She is nice and looks so young.She is a policewoman(女警察). She works in a police station(警察局). S
，其中
，则导数
的取值范围是
（B）. 
（C）
（D 
，∴
。