在平面直角坐标系中,点A(-1,0)与点B(0,2)的距离是______.
点A(-1,0)与点B(0,2)的距离是:(-1-0)2+(2-0)2=5.
故答案填:5.
海豚在水下通过发出一种声波的回声来判断附近物体的大小、形状和位置,海豚发出的是( )
A.频率低于20Hz的次声波
B.频率低于20Hz的超声波
C.频率高于20000Hz的次声波
D.频率高于20000Hz的超声波
根据下列句子的意思及所给的汉语提示,写出空缺处单词、固定短语或固定搭配的
正确形式。
1. People should be p______ from polluting the environment.
2. Could you write a ______ (describe) of your mother?
3. I think it is ______ (danger) for children to be close to wild animals.
4. Can you type and talk ______ (同时)?
5. Cathy was ill. So I went on business ______ (代替) her.