Today is Sunday. It's a nice day. Many people are at the ____. Some are playing volleyball. Some are ____shells and some are ____the sunshine. Peter is writing a ____.He wants to ____it in a bottle. Paul wants to know what it is about.
下列方程中是一元二次方程的是( )
选出读音全都正确的一组( )
带有编号1、2、3、4、5的五个球.
(1)全部投入4个不同的盒子里;
(2)放进不同的4个盒子里,每盒一个;
(3)将其中的4个球投入4个盒子里的一个(另一个球不投入);
(4)全部投入4个不同的盒子里,没有空盒;各有多少种不同的放法?