They are at home.
一般疑问句:Are they at home?
Ken is surfing the Internet.
一般过去式:Ken surfed the Internet.We were going to go skiing.用are改写句子We are going skiing.
The kitchen was messy.改成否定句The kitchen wasn't messy.
There was an egg in the nest.变为复数形式There were some eggs in the nests.