1.While the boy was playing in the garden,Iwas cooking in the kitchen[把I和boy调换也可]
2.He has gone to Australia several times[个人认为这句话有问题,应改为He has been to Australia for several times]
3.It is very cold outside,put your coat on.
[给点分吧,急用的]
I was cooking in the kitchen while the boy was playing in the garden.
或者
The boy was cooking in the kitchen while I was playing in the garden.
很多种组合
He has gone to Australia several times.
It is very cold outside, put on your coat.