I met him when he was walking  across the park.

Have you ever acted on the stage? — Why, yes, that's what I I have done  for the last six years.

Don't enter the bedroom! The child is sleeping there, and he always wakes up, when somebody opens the door

What WERE you DOING when I CAME in?  

When I CAME to his house, they TOLD me that he HAD LEFT an hour before.  

On checking up his answers he FOUND out that he HAD MADE several mistakes.  

When I LEFT (WAS LEAVING) home, the snow HAD already STOPPED, but a strong wind WAS BLOWING.  

HAVE you READ this book? — Yes, I HAVE READ it . I THINK it IS very interesting.  

What ARE the children DOING now? — Oh, they ARE PLAYING the new table game which I BOUGHT for them the day before  yesterday.  

They HAVE REACHED the corner of the street by now and ARE STANDING at the bus stop.