There are many students on the playground.Some are playing,others are standing in line.这句话对吗

问题描述:

There are many students on the playground.Some are playing,others are standing in line.这句话对吗
Some are playing,others are standing in line.这个中间缺少连词吧,是不是应该没有逗号的

我觉得对.逗号也是应该有的.句子没有什么毛病.